PHP Code:

$e["js_on_select_row"] = "grid_select";
$grid->set_events($e);

JS Code:

<script>
function grid_select()
{
var rowid = jQuery(this).jqGrid('getGridParam','selrow'); // returns null if no row is selected (single row)
//—–^—–
}
</script>

OR you can call:
var rowid = jQuery("#list1").jqGrid('getGridParam','selrow');
where list1 is grid id.

Dear Sir ,

Thanks Sir ..

And if I want to get other parameter than id when select that row ?

You can pass that rowid in getCell along with desired column name.

var rd = jQuery('#list1').jqGrid('getCell', rowid, 'invdate');

where list1 is grid id, invdate is column to fetch.