I have the following working function:
<script type="text/javascript">
function Handle_OnRowSelect(sender,args)
{
var _row = args["Row"];
var _dataitem = _row.getDataItem();
var $RowSelected= Number(_row);
}

</script>
How can I return the row number of the seleted row to PHP ?
Thank you.

You can call your PHP code from there:
...
window.open("HandleRowNumber.php?rowNumber=" + Number(_row), "_self");
...

Thank you Riho I will try this.