Seems to me there's no issue here with VORs, the issue is with interview technique. If you're asked a technical question, answer it to the best of your ability. If you're asked to go into more detail, answer by saying "I don't know the answer to that, the best I can do is give you an educated guess." If the interviewer invites you to make an educated guess, then do so, making sure you tell him why you think what you think.
For example, if I were asked in an interview why there are few VORs at high latitudes, I might explain to the interviewer that I wasn't aware that there were few VORs at high latitudes, but I could take a guess. Then, when asked further, I'd tell him that magnetic variation needs to be applied at the VOR sight, not at the aircraft. Normally, we don't need to worry too much about this, since the variation at the VOR will be so close to that at the aircraft it doesn't really matter. But at high latitudes, variation can change by many degrees in a relatively short distance, and this could cause confusion if variation isn't applied correctly.
I don't know if that's the right answer. (Is it?) But it shows that I understand how to apply variation at a VOR. It shows that I understand that there are parts of the world where variation is significant. And if it's not the correct reason, well, no problem because I told the interviewer beforehand that I didn't actually know the answer to the question.
This comes from being both interviewer and interviewee in the IT world - as interviewer, if a candidate demonstrates that they understand the principles then I will forgive them for not knowing the details of a small area. As interviewee, I've never had a problem getting job offers from interviews yet, so I assume I must be doing something right.
FFF
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