So after reading the story I have thought of some ideas about the themes.
1. Power- K. doesn't really have a say it is all what the court says, totalitarian government.
2. Justice- the legal system and how it works is very corrupt
3. sex- he sleeps with a lot of women who are affiliated with the court
4. isolation- K. seems very isolated and alone most of the time.
I have thought about all of these topics and the two that makes the most sense to me is Justice, and isolation.