Paul : " John, will you play tennis on Sunday?"
 
John is talking to his mother and says: "Paul asked (me) if I would play tennis on Sunday"

  "wh-questions" are reported as follows: ask

Sonia is talking to a friend about her holidays in Paris and says:  I asked a policeman where the Eiffel Tower was and he said it was  behind my back. It was so funny !

As you can see, when Sonia speaks to the policeman be is before the subject (interrogative form) because she is asking a question, but in the reported  question be is not in the interrogative form because the speaker (Sonia) is not asking a  question. She does not want an answer. She is reporting a question.

  ask (somebody) / want to know, etc. +  wh-word + verb ... (when the "wh- word" is the subject of the verb.)

Reporter to PC Smith: "Who killed Mr Rattle?"
 
PC Smith is speaking to his wife and says: "A reporter asked me who had killed Mr Rattle."