This has always been one of the big questions in Human Factors/CRM...
The most difficult bit is not really what the co-pilot should do but to actually get him/her to do it and to do it in the right situation. Far too many co-pilots have gone along for the ride straight into an accident they have seen coming.
Teneriffe comes to mind though mutiny would not have been needed there, much less the crash axe. According to people that knew him, captain Van Zanten was a very kind person and his behaviour just before the crash was very uncharacteristic of him. Yet both the co-pilot and the flight engineer failed to assert themselves enough to prevent the accident.
I don't think there is any simple answer to that kind of question on an interview, or a particular answer they are looking for.
You might possibly reply "I hope that I can judge that kind of situation correctly and be clear enough to begin with in getting the captain to understand that he is creating a dangerous situation."
I am, however, very interested in learning what others may have to say on the subject.