You are free to pick any project you want as long as it has a computer graphics related component in it. It can be some pet project you are working on at your free time, or something left unfinished in another course. For example, you can have projects from the CG course and CG seminar that you want to do additional work on. Project can also be related to your thesis work, if the latter includes a large development component.
If you do not have a pre-existing topic, then read on. Following is a list of sources, where you can find a good project topic.
Remarkable CGVR Projects
For inspiration you can see the awesome projects other students have done previously in this and other CG courses.
CG course projects.
In the CG course there were several proposed project topics with practical implications, which were not chosen. Furthermore some of the projects that were chosen can be continued. This means that you can contact the person responsible for some topic and propose further development.