Hi ahmadsubuhanlubis,

Refer below sample.

HTML

<asp:GridView runat="server" ID="gvCustomers">
    <Columns>
        <asp:TemplateField HeaderText="Name">
            <ItemTemplate>
                <asp:DropDownList ID="ddlName" runat="server">
                    <asp:ListItem Text="--Select Name--" Value="0" />
                    <asp:ListItem Text="John Hammond" Value="1" />
                    <asp:ListItem Text="Mudassar Khan" Value="2" />
                    <asp:ListItem Text="Suzanne Mathews" Value="3" />
                    <asp:ListItem Text="Robert Schidner" Value="4" />
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Country">
            <ItemTemplate>
                <asp:DropDownList ID="ddlCountry" runat="server">
                    <asp:ListItem Text="--Select Country--" Value="0" />
                    <asp:ListItem Text="USA" Value="1" />
                    <asp:ListItem Text="India" Value="2" />
                    <asp:ListItem Text="Russia" Value="3" />
                    <asp:ListItem Text="UK" Value="4" />
                </asp:DropDownList>
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<br />
<br />
<asp:Button ID="btnSubmit" Text="Submit" runat="server" OnClick="Submit" />
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/css/select2.min.css" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/js/select2.min.js"></script>
<script type="text/javascript">
    $(function () {
        $("[id*=ddlName]").select2();
        $("[id*=ddlCountry]").select2();
    });
</script>

Namespace

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[] { new DataColumn("Name2") });
        dt.Rows.Add("abc");
        gvCustomers.DataSource = dt;
        gvCustomers.DataBind();
    }
}
protected void Submit(object sender, EventArgs e)
{
    foreach (GridViewRow row in gvCustomers.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            DropDownList ddl = (DropDownList)row.FindControl("ddlName");
            DropDownList ddl2 = (DropDownList)row.FindControl("ddlCountry");
            string message = "Name: " + ddl.SelectedItem.Text;
            message += "\\nCountry: " + ddl2.SelectedItem.Text;
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('" + message + "')", 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() {New DataColumn("Name2")})
        dt.Rows.Add("abc")
        gvCustomers.DataSource = dt
        gvCustomers.DataBind()
    End If
End Sub

Protected Sub Submit(ByVal sender As Object, ByVal e As EventArgs)
    For Each row As GridViewRow In gvCustomers.Rows
        If row.RowType = DataControlRowType.DataRow Then
            Dim ddl As DropDownList = CType(row.FindControl("ddlName"), DropDownList)
            Dim ddl2 As DropDownList = CType(row.FindControl("ddlCountry"), DropDownList)
            Dim message As String = "Name: " & ddl.SelectedItem.Text
            message += "\nCountry: " & ddl2.SelectedItem.Text
            ClientScript.RegisterStartupScript(Me.[GetType](), "alert", "alert('" & message & "')", True)
        End If
    Next
End Sub

Screenshot