Code Behind:

   protected void gvCustomers_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName.Equals("RowSelected"))
            {
                GridViewRow row = (((e.CommandSource) as Button).NamingContainer) as GridViewRow;
                Label label = row.FindControl("lblFirstName") as Label;

                Response.Write(label.Text);

            }
        }

<asp:GridView AutoGenerateColumns="false" ID="gvCustomers" runat="server" OnRowCommand="gvCustomers_RowCommand" >

    <Columns>

    <asp:TemplateField>
    <ItemTemplate>

    <asp:Label ID="lblFirstName" runat="server" Text ='<%# Eval("FirstName") %>' />

    </ItemTemplate>
    </asp:TemplateField>

      <asp:TemplateField>
    <ItemTemplate>
    <asp:Button Text="Select" ID="btn1" runat="server" CommandArgument ='<%# Eval("FirstName") %>' CommandName="RowSelected" />
    </ItemTemplate>
    </asp:TemplateField>

    </Columns>

    </asp:GridView>

<asp:GridView ID="gvProduct" runat="server" AutoGenerateColumns="False" DataKeyNames="ID"OnRowCommand="gvProduct_RowCommand" >
<Columns>
   <asp:TemplateField>
       <ItemTemplate>
           <asp:ImageButton ID="btnEdit" runat="server" CommandName="EditCommand" Text="Edit" />
       </ItemTemplate>
   </asp:TemplateField>
<asp:BoundField DataField="ProjectNo" HeaderText="ProjectNo" />
<asp:BoundField DataField="Date" HeaderText="Date" />
<asp:BoundField DataField="Shift" HeaderText="شیفت" />
</Columns>
</asp:GridView>

protected void gvProduct_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "EditCommand")
        {
            GridViewRow Row = (GridViewRow)((Control)e.CommandSource).NamingContainer;
            int productID = Convert.ToInt32(gvProduct.DataKeys[Row.RowIndex].Value);

            EditFunction(productID);
        }
    }