So, "ask me a question" is correct, "ask me of (a) question" would be incorrect. However, the sentence you gave is a structured a little differently.

It means "If you ask a question about and potentially to one volunteer, you must ask..."

As a person, I can ask a question to someone. The person must be able to hear me in some capacity (in front of me or on the phone) for this to make sense.

I can also ask a question about someone. In this case, the person I'm asking about does not need to be able to hear me at all; I'm not speaking to them. For example, I could ask my mother about the president's health is doing.

I believe when you ask a question of someone, that it's likely about that person, and may also be directed towards them. For example, you may be asking a volunteer if they've passed a background check. I would say that is asking a question of them.

Perhaps more practically, I consider my native literacy somewhere in the very center of all people, and I don't think I've ever said or written "asking a question of" someone. I would simply ask a question "to" or "about" someone. That said, the sentence you gave is correct.