print Gridview data

Either you can write your print related code in code behind and then inject it into the page:
How to Print in ASP.NET 2.0[^]

OR using JavaScript directly on the page itself, like:

function CallPrint()
{
  var printContent = document.getElementById('<%= pnlToPrint.ClientID %>');
  var printWindow = window.open("", "Print Panel", ‘left=50000,top=50000,width=0,height=0′);
  printWindow.document.write(prtContent.innerHTML);
  printWindow.document.close();
  printWindow.focus();
  printWindow.print();
  printWindow.close();
}

<asp: Panel runat="server" id="pnlToPrint" >
  <table>
    <tr>
      <td>
         Your data
      </td>
    </tr>
  </table>
</asp: Panel>

<input type="button" value="Print"  onclick="CallPrint();" />

Above code prints just the content inside the panel - can be a grid or even just a label.