Computer science is a very rich and interdisciplinary field. If you can think of some study you'd wish to pursue, it's probably already there. However, from another CS major's point of view, some subfields to look out for:

Artificial intelligence and machine learning: We've got the basics down, but research into better methods of training ML models in different environments offers a lot of promise.

Parallelism and scheduling: if you like systems, parallelism studies how to assign parallel threads to the multi-core processors in your computer. The study will be increasingly useful as we approach the asysmptote of Moore's Law. Study functional languages, systems, and concurrency.

NLP and law studies: if natural language processing is your thing, try working with lawyers. Their job requires them to review hundreds and thousands of documents on legislation, previous rulings and precedents, and plain old red tape. Developing a system to automate the review process would be indispensible to lawyers and paralegals.

Of course, the subfield you pursue should be interesting to you. Talk with a beloved professor or an advisor for guidance. Note if you enjoy one class or another. And enjoy your learning! Good luck!

Bioinformatics. The amount of deep sequence and next gen data is enormous - we are drowning in it. Every challenge of computing is pretty much present in the biol space - some of the ones that come to mind include how we address huge data sets, and lots of them, predict structures of components such as genomic spacial arrangement, protein structures and rna folding.

There are areas associated with massively parallel computing and storage, interface (allowing biologists to use complicated analytical tools), collaboration, rdbms and nonrdbms, language and algorithm optimisation.

It is massive and constantly evolving