Move jquery ui to footer

Ok i found alone the solution, the problem was that it is ‘jquery-ui-core’ and not ‘jquery’.
Thank you a lot for the effort

P.S: In order not to open second similar thread, how do i find the theme js libraries and put them to footer, for example i have http://example.com/wp-content/themes/theme-name/js/dropdown.js and i want to move it to footer. If i use enqueue, it becomes double, one in header and one in footer. Basically i don’t know where to go and find its handle name