How to get from Dusseldorf Airport to Bochum University campus, by public transport, train or bus? I plan to go there early October 2015.
You take the train from Düsseldorf Airport to Bochum Hbf (main station) and change there to subway line U35, which will take you to the university. There are 3-4 trains per hour and the subway departs every five minutes, or even more often during rush hours. If you have a few minutes to spare, you might prefer the regional trains from Düsseldorf Airport to Bochum Hbf, as they are slightly cheaper (13.70€ vs 19.00€), but almost just as fast as the long distance trains.
You can search for available connections using the German Railway's trip planner.