grammar - When can we omit "does" in the question sentence

I am learning Duolingo English course, I saw a sentence like this:

Who uses the wheels?

But should we use something below?

Who does use the wheels?

What's difference between two? When can I omit the word does in a question sentence?

Thanks

Jake

Answer

Without negation, does is used to question the truth of a statement, or to add emphasis. For example:

Does she use the wheels? Yes/No/I don't know

In your example, you're not asking about whether someone uses the wheels or not, but who uses the wheels, if anyone does at all. For instance:

Who uses the wheels? I do/she does/Alice does/Bob does

Does can also be used for emphasis in certain variants of English (US, UK, Aus, Canadian). For example:

Alice: "She doesn't use the wheels."

Bob: "Who does use the wheels?"

In this case, the use of does would be accompanied by a pitch movement, to show emphasis, usually with it being pronounced with a higher pitch than the rest of the sentence.