It's necessary for one massive reason. You will inevitably come into problems, and then you will be glad to have a good understanding of JavaScript.
nah you don't _have_ to. plenty of designers and suchlike use jquery daily w/o having a clue. and that's ok - but if you're a web dev ... just be prepared that one day you may get a question at an interview like what is getElementById and 50% of jquery `users` will think twice about that (or if pushed, the difference between that and $("#id"))
yes.. it would be an advantage. javascript knowledge will definetly help you one day if you're a developer.