Pointing to a photograph John said, "She is the only granddaughter of the husband of my mother's sister." How is the person in the photograph related to John.

John's mother's sister → (This is John's maternal aunt.)
Husband of John's maternal aunt → (This is John's maternal uncle.)s son or daughter).)
John's maternal uncle’s son or daughter is John's cousin.
Only granddaughter of John's maternal uncle → (This means the girl in the photograph is the daughter of John's cousin.)

According to the given information, Family tree diagram will be:

As per the diagram , the person in the photograph is John's maternal uncle’s daughter.

Therefore, Cousin’s daughter is John's niece.

Thus,the correct option is (c) Niece