I'm getting my upper left wisdom tooth out. Will they have to cut my gum to get the rest of the tooth that hasnt fully come out yet?

Yes. Yes, if not fully erupted (impacted) and incision is required. For best results, make sure you are evaluated and treated by a board certified oral & maxillofacial surgeon.
Perhaps. Sometime yes and sometimes no. However, if they do have to make any incisions, it only makes the removal easier and therefore less discomfort for you afterwards. Trust and leave it up to your surgeon.