Make a questions without auxiliary verb

All main clause interrogatives but those questioning the subject have subject-auxiliary inversion and those lacking an auxiliary verb require the addition of dummy-do.

How do you answer this question?

Who do you know best?

Do I know you?

He went home.

He did go home.

Did he go home?

We question the subject using interrogative words who, which or what only. We may use an auxiliary verb, but there is no inversion.

Who came back early?

Who can come back early?

What dropped from the tree?

What did drop from the tree?

Which (shop) has the best apples?

Which (shop) will have the best apples?