I am working on my doctoral thesis and I want to present my thesis project, but I also want to present a research work already done. Do I have to register for the International Conference of Doctoral Students and also for the Congress?

No. You cannot register and/or present your work simultaneously in the International Doctoral Student’s Workshop and in the Congress both scientific events take place in the same time. Therefore, you have to decide in which of the two events you are interested in registering.