Nuuk is not 62 degrees north if you google Nuuk and latitude - quite a few sites show it as 64 degrees plus. My Phillips world atlas shows them both as being 64 10 so to me its a VERY difficult question to answer. Googling northernmost capital does indeed come up with Reykjavik nearly 100% but this appears to me to be open to debate.
If I'm not mistaken, this is from a charity quiz and, by answering the other questions, it becomes obvious that the answer in this case begins with the letter R
Surely a key point is that Greenland is not wholly independent, since Denmark - its coloniser - is still responsible for its foreign policy. Accordingly, I'm sure people could legitimately claim that it is not a 'country' at all and therefore does not have a capital in any real sense. People speak of Albany as the 'capital' of New York State, but it really means only 'administrative centre'.