No need to add this file add any jquery file .You can get it from
www.jquery.com
You can also try this
Html Code
<input id="txtText" type="text" value="<%=DateTime.Now.ToShortDateString() %>" onclick="return CheckData(this);" />
Script
<script type="text/javascript">
function CheckData(text) {
$(text).val('');
};
</script>