Q:

jQuery on() method - which way to use is better for performance?

Is it better to attach the on() event to the document or a closer parent?
Note: Initially this question had another aspect and a different topic. It became obsolete really quickly (typo in the source code)

A:

The best key for performance using jQuery is to use an id as the initial identifier. For example:
$('#my_id').on('click', 'tag.my_class', function () {
    ...
});

This allows jQuery to go straight to the container, and then begin trawling from there. 

