Contact Form 7 jQuery hooks

After a ton of research, I’m having a heck of a time finding any guide to adding a simple jQuery hook to a change in a Contact Form 7 form.

What I’m looking for is simple (I think) – an onChange event for a dropdown that yields a popup saying “dropdown has changed”. I’ve seen a number of posts with no responses, as well as people posting vague comments like “just use jQuery” – does anyone have any practical advice on where to put what in order to achieve something simple like this?