Sorry. I didn't asked the right question. My bad 
Jquery.Validity uses the component id/name selector to check required
$('#myinput').require('this field is required');
$("[name='myinput']").require('this field is required');
this works fine in Appery.io.
in the case of the date picker, it looks like it uses a text input component to store the selected date. It looks like this input doesn't have an name or an id to use. i.e. it doesn't use the name of the mobiledatepicker.
I'm sure I can write something custom for dates using the getAttr, like you suggest here. However, I was hoping not to have to. Lazy 
Any ideas?