If P is the maternal uncle of Q, how is Q related to P's sister?

If P is the maternal uncle of Q, then P is the brother of Q’s mother.

However, the phrase “P’s sister” is not precise enough. It may refer to Q’s mother, in which case Q is her son/daughter, or it may refer to another sister of P, in which case Q is her niece/nephew. The gender of Q is also not given.

Correct answer: Cannot be determined.