谁的【shéi de】

shéi谁de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 leaves 的 with no noun after it, which is normal: 谁的 on its own works like English "whose" without a noun.

Answering

The answer copies the shape of the question and usually drops the noun.

谁 or 谁的

shéi谁 asks which person; 谁的 asks which person something belongs to.

Common mistakes

The 的 cannot drop, and the sentence takes no 吗, because 谁 already makes it a question.

• × 这是谁书？ → 这是谁的书？
• × 这是谁的书吗？ → 这是谁的书？