You can use the setGridParam method to register the beforeSelectRow event beforeSelectRow in an existing grid. This handler must return false to cancel the select operation.
In your case, you can use the is () method on target to determine if a click on the checkbox has been set. The end result will be something like:
$("#yourGrid").jqGrid("setGridParam", { beforeSelectRow: function(rowId, e) { return $(e.target).is("input:checkbox"); } });
source share