Hi,
Please try below code.
<script type="text/javascript">
$(function () {
$('[id*=btnAdd]').on('click', function () {
var count = parseInt($(this).closest('td').find('[id*=txtOrderQty]').val()) || 0;
$(this).closest('td').find('[id*=txtOrderQty]').val(count + 1);
return false;
})
});
</script>
I hope this will help you out.