I've been told that it is okay to say "What can I do you for?" instead of "What can I do for you?" and in fact I myself have heard people say that many times.
So, if it's correct, would "you" be a direct object in that case or still indirect like in "What can I do for you?"
By the way, if it's not a big trouble for you, please, tell me if my punctuation in the end of the title is correct.
In my experience "What can I do you for" is a joke that became a catch-phrase and entered some people's everyday vocabulary. It stands for "what can I do for you".
The literal meaning is about "doing (someone) for (something)", which in British usage means prosecuting them at law. "He got done for dangerous driving". In this literal phrase, yes "you" would be the direct object.
"What can I do for you" is of course a common phrase offering a service, and "you" is at best an indirect object, probably only an adjunct.
Note: the previous discussion, that Peter of the Corn linked to, refers to a number of different colloquial meanings of "do someone"; but it seems to me that most of them are not relevant, because they are "do someone", not "do someone for something".
You is a direct object in what can I do you for?, where do is the action directly performed on you. See this answer which clarifies the meaning of the do you in what can I do you for?
And the question mark and quotation thing should be changed to ...in "What can I do you for"?
"What can I do for you?" is a more common, standard, acceptable and grammatically correct question compared to "What can I do you for?" Therefore it is preferable to use the former. And the punctuation you used in the title is okay.
