Hi ahmadsubuhanl...,

Refer below example.

HTML

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" DataKeyNames="Name">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:TemplateField HeaderText="Country">
            <ItemTemplate>
                <asp:TextBox ID="txtCountry" runat="server" Text='<%# Eval("Country") %>'></asp:TextBox>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<br />
<asp:Button Text="Get" runat="server" OnClick="GetDetails" />

Namespaces

C#

using System.Data;

VB.Net

Imports System.Data

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] {
            new DataColumn("Id"),
            new DataColumn("Name"),
            new DataColumn("Country")
        });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

protected void GetDetails(object sender, EventArgs e)
{
    foreach (GridViewRow row in GridView1.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            string name = GridView1.DataKeys[row.RowIndex].Values[0].ToString();
            string country = (row.Cells[2].FindControl("txtCountry") as TextBox).Text;
            ClientScript.RegisterClientScriptBlock(this.GetType(), "alert" + row.RowIndex,
                "alert('" + string.Format("Name:{0}\\nCountry:{1}", name, country) + "');", true);
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {New DataColumn("Id"), New DataColumn("Name"), New DataColumn("Country")})
        dt.Rows.Add(1, "John Hammond", "United States")
        dt.Rows.Add(2, "Mudassar Khan", "India")
        dt.Rows.Add(3, "Suzanne Mathews", "France")
        dt.Rows.Add(4, "Robert Schidner", "Russia")
        GridView1.DataSource = dt
        GridView1.DataBind()
    End If
End Sub

Protected Sub GetDetails(ByVal sender As Object, ByVal e As EventArgs)
    For Each row As GridViewRow In GridView1.Rows
        If row.RowType = DataControlRowType.DataRow Then
             Dim name As String = GridView1.DataKeys(row.RowIndex).Values(0).ToString()
            Dim country As String = (TryCast(row.Cells(2).FindControl("txtCountry"), TextBox)).Text
            ClientScript.RegisterClientScriptBlock(Me.GetType(), "alert" & row.RowIndex, "alert('" & String.Format("Name:{0}\nCountry:{1}", name, country) & "');", True)
        End If
    Next
End Sub

Screenshot