谁【shéi】

谁 asks "who", and it stands in the slot the answer would fill.

Chinese makes no distinction between "who" and "whom" – 谁 covers both, because it simply sits wherever the person belongs.

Two pronunciations

谁 is read shéi or shuí. shéi is what you hear in conversation; shuí belongs to careful reading and to formal speech. Same character, same meaning.

After a preposition

谁 keeps its place there as well, in front of the verb along with the preposition.

谁的 asks whose

No 吗

shéi谁shì是nǐ你de的lǎo shī老师má吗 is wrong – 谁 has already made it a question.

谁 as "anyone" and "everyone"

With 都 or 也 after it, 谁 stops asking and means "everybody" or, under negation, "nobody".