Hi NG
You are right. Indirect questions fall in three categories.
1. There is a word that can begin a clause but the word is not the subject.
What did he say? - Tell me what he said.
2. There isn't a word that can begin a clause. If or whether must be used.
Did he come in time? - Tell me if/whether he came in time .
3. A question word - in Scandinavia we call them interrogative pronouns - is the subject or a part of the subject.
What is wrong with this? - Tell me what is wrong with this.
Whose friend saw it? - Tell me whose friend saw it.
Because the interrogative word is the grammatical subject of the clause, there is no change in the word order.
CB