Accessing data of grid view row whose check box is checked

protected void Button1_Click(object sender, EventArgs e)
{          
   SqlConnection conn = new SqlConnection();
   conn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["yourstring name"].ConnectionString;
   conn.Open();
   DataTable dtable = new DataTable();
   dtable.Columns.Add(new DataColumn("field name", typeof(string)));
   //Define datatable based on your requirement
   Session["dt"] = dtable;
   foreach (GridViewRow gvrow in yourgridview.Rows)
   {
    CheckBox chk = (CheckBox)gvrow.Cells[3].FindControl("yourcheckbox");//checkbox is in  4th column,hence Cells[3]               
      if (chk != null && chk.Checked)
      {
            dtable=(DataTable)Session["dt"];
            DataRow dd = dtable.NewRow();
            dd["field name"] = (gvrow.Cells[1].Text);//store data appropriately            
            dtable.Rows.Add(dd);
            GridView1.DataSource = dtable;//getting data in another gridview
            GridView1.DataBind();                        
            Session["dt"] = dtable;
     }
  }
}