<script type="text/javascript" src="//use.typekit.net/xxxxxx.js"></script>
At a minimum this needs to remain in head.php. Loading a script src is different than running JS code.
There’s no reason you couldn’t put this:
try{Typekit.load();}catch(e){}
In /assets/js/_main.js but you probably don’t want to do that. You need that code to run ASAP after the Typekit script is loaded.
Basically, keep them where they are 