Learn Turkish: Uşak için özel masör mü? - A private masseur for the butler?

This is a rhetorical echo question. The speaker is repeating a noun phrase they just heard and attaching the question particle mü directly to it to express disbelief. Because it is a shocked reaction rather than a standard seeking of information, no verb is needed. You are simply echoing the concept back!

If I wanted to express shock that the butler is getting the masseur (and not someone else), how would I change this sentence?

The question particle always follows the specific element you are doubting or emphasizing. To express shock that it is for the butler, you would move the particle right after that phrase: Uşak için mi özel masör?

Why is there no bir (a/an) before özel masör?

In fast, emotional echo questions, speakers often strip the phrase down to the bare essentials they are reacting to. Dropping bir emphasizes the sheer absurdity of the concept (hiring a private masseur) rather than focusing on a singular countable person.

Doesn't özel usually mean "special"? Why is it translated as "private" here?

Yes, özel means both "special" and "private" depending on the context. Just as özel okul means "private school" and özel hayat means "private life", an özel masör in this context implies a privately hired masseur for personal use.