Can anyone give me a "to what extent" question on the four voyages of Christopher Columbus?
You could go a number of different ways with this. In general, what you want to do with a question like this is to find some aspect of the person's (Columbus, in this case) reputation and ask about the extent to which it is deserved.
So, you could ask something like "To what extent does Columbus deserve to be seen as a great explorer?" That would cover things like the fact that he did "discover" the Americas but did so by accident. Or, you could ask "To what extent does Columbus deserve to be criticized for what happened to the Native Americans at the hands of the Europeans?" This would cover the controversy over whether Columbus should be seen as an agent of genocide. One last one might be "To what extent would the world be different if Columbus's voyages had never happened?" This would make people think about what impact the voyages had and perhaps about whether the same things would have happened without Columbus.