fisrt Add Gridview select button
when u r binding gridview that time store ur data table in viewState{"data"]
Grid Have row command evevnt
protected void Grid1_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Select")
{
int num = Convert.ToInt32(e.CommandArgument);
// u will get selected row number in num
//suppose ID column present in data table now u can easily fetch value using following
DataTable dt=ViewState["data"] as DataTable;
string s=dt.Rows[num]["ID"].toString();
}
}