Answer:
Julia lebt in Gießen.
Claudia lebt in Bernau.
David lebt in Marburg.
Explanation:
In the text, it says that Julia lives in Giessen, Claudia lives in Bernau, and David lives in Marburg. So, we can answer the question of where do they all live, by reading the text. Of course, you have to put your answer in German as well, so I have done that.