"Do you know Geography?"
Yes, because using the definite article when you talk about something non-specific is wrong (the question above talks about geography in general, without any other context). If the question was "Do you know Greece's geography?" then an article would be needed, because you are talking about a particular geography. Ξέρεις την γεωγραφία της Ελλάδας;
Would you still need the definite article in the nominative? For example "μου αρέσει η Γεωγραφία" ?