[mohawk]

Your question is hard to answer because it's not clear what your goal is. More math is always useful, but you wrote you already have a solid background there. Public speaking, communication, and "people skills" in general are always good to have and might become more important later on in your career.

If you want a fun list of topics, here are some off the top of my head that i might look at in your situation:

- fully homomorphic encryption

- recurrent neural networks & machine learning

- proving computer programs correct & computer-aided mathematical proofs