Foren / Cotonti / Extensions / [Q] How to Integrate the jQuery api / How to Tag?

jQuery is just jQuery, so the best is jQuery Docs. If you wonder what is special for Cotonti, take a look at js/base.js (though it is not very jquerish).

As for tags, you can find API reference in code reference, a series of function named sed_tag*. A good example of its use is the plugins/tags itself because it is implemented as a plugin for that API.