A test paper is asking me to state what rules are broken. I am stuck on explaining - could anybody help me please?

He asked what do I earn (keep in indirect form)

I know it should read - He asked what I earn. I see a double use of verbs in the sentence but am struggling to give a better explaination.

Indirect questions never take the auxiliary do.

What do I earn? - This is a direct question.
He asked what I earn. - what I earn is an indirect question within the larger sentence.


What language do you speak?
I asked him what language he spoke.

Which one do you like best?
I can't decide which one I like best.

Thanks CJ - That makes sense now.