Thanks for A2A. This question could be better answered by Google though.
There is a huge list of topics but I will try and mention as many as possible.
- Programming Languages.i.e C,C++,Java etc.
- Digital Electronics
- Data Structures
- Algorithm Design and Analysis.
- Discrete Mathematics.
- Graph Theory and combinatorics
- Computer Organisation and Architecture
- Operating Systems
- Compiler Design
- DataBase Management
- Theory of Computation
- Micro Processors