What topic is interesting to you? If you have no idea, change to another degree area - CS is not for you. CS has a huge number of subject areas that need investigation and work. Find something that is of interest to you.
I have worked in development framework architecture, design, and implementation along with garbage collection (having implemented a deterministic real-time garbage collector in C++), performance engineering (wrote tools to collect 10 billion data points per day from 5000+ servers to store in a hadoop database, along with many analytical tools for that data), parsers, database-neutral API's (ODBC before ODBC), TCP/IP implementations from the White Book specifications, etc.
Picking a topic that interests you is the key here. If you aren't passionate about the topic, or at least interested/curious, then you won't produce a paper that will do you credit. That, we cannot help you with.