Hi akhter,

use common class name to select the TextBox for compare.

Refer below sample code.

HTML

<asp:GridView ID="GridviewN" runat="server" ShowFooter="true" AutoGenerateColumns="false" DataKeyNames="ID" CssClass="Highlight">
    <Columns>
        <asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True" SortExpression="ID" />
        <asp:TemplateField HeaderText="N 1">
            <ItemTemplate>
                <asp:TextBox ID="PackNo" Width="54px" runat="server" Text='<%#Bind("PackNo")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 2">
            <ItemTemplate>
                <asp:TextBox ID="PackNo1" Width="54px" runat="server" Text='<%#Bind("PackNo1")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 3">
            <ItemTemplate>
                <asp:TextBox ID="PackNo2" Width="54px" runat="server" Text='<%#Bind("PackNo2")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 4">
            <ItemTemplate>
                <asp:TextBox ID="PackNo3" Width="54px" runat="server" Text='<%#Bind("PackNo3")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 5">
            <ItemTemplate>
                <asp:TextBox ID="PackNo4" Width="54px" runat="server" Text='<%#Bind("PackNo4")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 6">
            <ItemTemplate>
                <asp:TextBox ID="PackNo5" Width="54px" runat="server" Text='<%#Bind("PackNo5")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 7">
            <ItemTemplate>
                <asp:TextBox ID="PackNo6" Width="54px" runat="server" Text='<%#Bind("PackNo6")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 8">
            <ItemTemplate>
                <asp:TextBox ID="PackNo7" Width="54px" runat="server" Text='<%#Bind("PackNo7")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 9">
            <ItemTemplate>
                <asp:TextBox ID="PackNo8" Width="54px" runat="server" Text='<%#Bind("PackNo8")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="N 10">
            <ItemTemplate>
                <asp:TextBox ID="PackNo9" Width="54px" runat="server" Text='<%#Bind("PackNo9")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<hr />
<asp:GridView ID="GridviewC" runat="server" ShowFooter="true" AutoGenerateColumns="false" DataKeyNames="ID" CssClass="Highlight">
    <Columns>
        <asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True" SortExpression="ID" />
        <asp:TemplateField HeaderText="C 1">
            <ItemTemplate>
                <asp:TextBox ID="PackNo" Width="54px" runat="server" Text='<%#Bind("PackNo")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 2">
            <ItemTemplate>
                <asp:TextBox ID="PackNo1" Width="54px" runat="server" Text='<%#Bind("PackNo1")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 3">
            <ItemTemplate>
                <asp:TextBox ID="PackNo2" Width="54px" runat="server" Text='<%#Bind("PackNo2")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 4">
            <ItemTemplate>
                <asp:TextBox ID="PackNo3" Width="54px" runat="server" Text='<%#Bind("PackNo3")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 5">
            <ItemTemplate>
                <asp:TextBox ID="PackNo4" Width="54px" runat="server" Text='<%#Bind("PackNo4")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 6">
            <ItemTemplate>
                <asp:TextBox ID="PackNo5" Width="54px" runat="server" Text='<%#Bind("PackNo5")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 7">
            <ItemTemplate>
                <asp:TextBox ID="PackNo6" Width="54px" runat="server" Text='<%#Bind("PackNo6")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 8">
            <ItemTemplate>
                <asp:TextBox ID="PackNo7" Width="54px" runat="server" Text='<%#Bind("PackNo7")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 9">
            <ItemTemplate>
                <asp:TextBox ID="PackNo8" Width="54px" runat="server" Text='<%#Bind("PackNo8")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="C 10">
            <ItemTemplate>
                <asp:TextBox ID="PackNo9" Width="54px" runat="server" Text='<%#Bind("PackNo9")%>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        HighlightDuplicate('.Highlight');
    });

    function HighlightDuplicate(gridView) {
        var inputs = $(gridView).find('input');
        for (var i = 0; i < inputs.length; i++) {
            for (var j = 0; j < inputs.length; j++) {
                if (inputs[i] != inputs[j]
                    && (inputs[i].value != "" || inputs[j].value != "")
                    && inputs[i].value == inputs[j].value) {
                    inputs[i].style.backgroundColor = "yellow";
                    inputs[j].style.backgroundColor = "yellow";
                    inputs[i].parentNode.bgColor = "red";
                    inputs[j].parentNode.bgColor = "red";
                }
            }
        }
    }
</script>

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        System.Data.DataTable dt = new System.Data.DataTable();
        dt.Columns.AddRange(new System.Data.DataColumn[11] {
        new System.Data.DataColumn("ID"),
        new System.Data.DataColumn("PackNo"),
        new System.Data.DataColumn("PackNo1"),
        new System.Data.DataColumn("PackNo2"),
        new System.Data.DataColumn("PackNo3"),
        new System.Data.DataColumn("PackNo4"),
        new System.Data.DataColumn("PackNo5"),
        new System.Data.DataColumn("PackNo6"),
        new System.Data.DataColumn("PackNo7"),
        new System.Data.DataColumn("PackNo8"),
        new System.Data.DataColumn("PackNo9") });
        dt.Rows.Add(1, 1, 1, 1, 1, 1, 1, 1, 444, 1, 1);
        dt.Rows.Add(2, 555, 555, 1, 1, 1, 666, 1, 888, 1, 1);
        dt.Rows.Add(3, 1, 1, 1, 2, 444, 1, 1, 555, 1, 1);
        dt.Rows.Add(4, 1, 1, 1, 1, 222, 1, 444, 1, 1, 1);
        GridviewN.DataSource = dt;
        GridviewN.DataBind();

        dt.Clear();
        dt.Rows.Add(1, 1, 1, 1, 1, 1, 222, 1, 444, 1, 1);
        dt.Rows.Add(2, 555, 555, 1, 1, 1, 777, 1, 1, 1, 1);
        dt.Rows.Add(3, 1, 1, 1, 2, 444, 1, 1, 555, 1, 1);
        dt.Rows.Add(4, 1, 333, 1, 1, 1, 1, 444, 1, 1, 1);
        GridviewC.DataSource = dt;
        GridviewC.DataBind();
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not Me.IsPostBack Then
        Dim dt As Data.DataTable = New Data.DataTable()
        dt.Columns.AddRange(New Data.DataColumn(10) {
                            New Data.DataColumn("ID"),
                            New Data.DataColumn("PackNo"),
                            New Data.DataColumn("PackNo1"),
                            New Data.DataColumn("PackNo2"),
                            New Data.DataColumn("PackNo3"),
                            New Data.DataColumn("PackNo4"),
                            New Data.DataColumn("PackNo5"),
                            New Data.DataColumn("PackNo6"),
                            New Data.DataColumn("PackNo7"),
                            New Data.DataColumn("PackNo8"),
                            New Data.DataColumn("PackNo9")})
        dt.Rows.Add(1, 1, 1, 1, 1, 1, 1, 1, 444, 1, 1)
        dt.Rows.Add(2, 555, 555, 1, 1, 1, 666, 1, 888, 1, 1)
        dt.Rows.Add(3, 1, 1, 1, 2, 444, 1, 1, 555, 1, 1)
        dt.Rows.Add(4, 1, 1, 1, 1, 222, 1, 444, 1, 1, 1)
        GridviewN.DataSource = dt
        GridviewN.DataBind()
        dt.Clear()
        dt.Rows.Add(1, 1, 1, 1, 1, 1, 222, 1, 444, 1, 1)
        dt.Rows.Add(2, 555, 555, 1, 1, 1, 777, 1, 1, 1, 1)
        dt.Rows.Add(3, 1, 1, 1, 2, 444, 1, 1, 555, 1, 1)
        dt.Rows.Add(4, 1, 333, 1, 1, 1, 1, 444, 1, 1, 1)
        GridviewC.DataSource = dt
        GridviewC.DataBind()
    End If
End Sub

Screenshot