Sentence question

Do you know how much she charges for a haircut? is correct. There is no subject-auxiliary inversion in subordinate interrogative clauses (a.k.a. indirect questions).

Thanks.

Aspara GusThere is no subject-auxiliary inversion in subordinate interrogative clauses (a.k.a. indirect questions).

What does that mean? Is it something regarding the second sentence? Can you please indicate what you mean?

I am guessing that you mean 'does' should not be used in these sentence, but please clarify.

How much does she charge for a haircut? - Direct Question
I don't know how much she charges for a haircut. - This is a statement, not a direct question. The part in blue is only a subordinate clause within that statement.
Do you know how much she charges for a haircut? - This is a direct question,

fivejedjonThis is a direct question, but the part in blue is only a subordinate clause within that question. It is not itself a direct question. The direct question is Do you know X?, in which X is the subordinate clause.

Thank you so much fj. That was very helpful. So this last example is like taking part of the second example (statement) and putting it into

Yes.