谁的 + [noun]? [noun] + 是谁的?
谁的 asks whose something is. It is 谁 plus the possessive 的, and it sits either before the noun or at the end after 是.
The two orders differ only in emphasis. The second one leaves 的 with no noun after it, which is normal – 谁的 on its own means "whose one".
The answer copies the shape of the question and usually drops the noun.
谁 asks which person; 谁的 asks which person owns it.