Please use “gridComplete” event. Example

$(document).ready(function() {
$(“#your_grid_id”).jqGrid(‘setGridParam’,{
gridComplete: function(){
// your custom jquery here
}
});
});

Use custom event handler support will be added in the future release.

Update:

Please see this KB for server side approach using add_event() method.
http://phpgrid.uservoice.com/knowledgebase/articles/319306