Normally, you should know how to respond to it. We're going to look into how the auction progresses after the response.
Remember the responses to 4NT, when a trump suit is agreed:
4NT -
5♣ - 3 or 0 keys
5♦ - 4 or 1 key(s)
5♥ - 2 keys without the Queen of trumps
5♠ - 2 keys with the Queen of trumps
