Yes. You can either go to a docent’s office hours or send her/him an e-mail. It is advantageous to contact docents who you know from pro-/seminars or lectures. However, it is your decision, who you ask.
In case you want to get an overview of potential topics, you might also approach several docents. But:
If you have found an adequate topic under supervision of one of the docents, tell the other docents!
This is not only a gesture of politeness but also an act of thoughtfulness towards your fellow students who now can write their theses on one of your rejected topics.