But have you linked in your jQuery library? Just because closest is a function within jQuery – if it can’t find that function then my first thought is whether the library has been pulled in?
I’m pretty sure it loaded. The files (.js) show up in the head of the page for the bubbuleup function, so it appears to be calling it properly. Also it is performing half of the function, which adds a tooltip, but then it fails there. I’m using Drupal’s built in jquery library, but I also tried linking to the library that is in Lam’s tutorial, but unless I did it wrong, it made no difference.