Hi kankon,

Refer below code.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

<form id="form1" runat="server">
    <asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
        Font-Names="Arial" Font-Size="10" RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White"
        AlternatingRowStyle-ForeColor="#000" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:TemplateField HeaderText="City">
                <ItemTemplate>
                    <asp:Label ID="txtName" Text='<%# Eval("ContactName") %>' runat="server" Width="120" />
                    <asp:Button ID="btnShow" runat="server" Text="Show Text" Width="120" OnClick="btnShow_Click" />
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
</form>

Namespaces

 C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

VB.Net

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid()
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT TOP 5 ContactName FROM Customers"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                }
            }
        }
    }
}

protected void btnShow_Click(object sender, EventArgs e)
{
    GridViewRow row = (sender as Button).NamingContainer as GridViewRow;
    string name = (row.FindControl("txtName") as Label).Text.Trim();
    ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('" + name + "')", true);
}

VB.Net

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then
            Me.BindGrid()
        End If
    End Sub

    Private Sub BindGrid()
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using con As SqlConnection = New SqlConnection(constr)
            Using cmd As SqlCommand = New SqlCommand("SELECT TOP 5 ContactName FROM Customers")
                Using sda As SqlDataAdapter = New SqlDataAdapter()
                    cmd.Connection = con
                    sda.SelectCommand = cmd
                    Using dt As DataTable = New DataTable()
                        sda.Fill(dt)
                        GridView1.DataSource = dt
                        GridView1.DataBind()
                    End Using
                End Using
            End Using
        End Using
    End Sub

    Protected Sub btnShow_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim row As GridViewRow = TryCast((TryCast(sender, Button)).NamingContainer, GridViewRow)
        Dim name As String = TryCast(row.FindControl("txtName"), Label).Text.Trim()
        ClientScript.RegisterClientScriptBlock(Me.GetType(), "", "alert('" & name & "')", True)
    End Sub

Screenshot

kankon says:

 DataTable dt = new DataTable();

           dt.Columns.AddRange(new DataColumn[1] {

           new DataColumn("mobile")});

 

           string mobile = (FindControl("mobiletxt") as Label).Text.Trim();

           dt.Rows.Add(mobile);

           string url = string.Format("https://api.whatsapp.com/send?phone=00965{0}&text=&source=&data=&app_absent=/Insert", "mobiletxt");

                   System.Diagnostics.Process.Start(url);

               }

You need fetch the number from select row on button click and pass it to the url.

protected void Button48_Click(object sender, EventArgs e)
{
    GridViewRow row = (sender as Button).NamingContainer as GridViewRow;
    string mobile = (row.FindControl("mobiletxt") as Label).Text.Trim();
    string url = string.Format("https://api.whatsapp.com/send?phone=00965{0}&text=&source=&data=&app_absent=/Insert", mobile);
    System.Diagnostics.Process.Start(url);
}