Learn English – Handling quotes ending in exclamation or question marks

The APA Style Guide is not a legal text trying to cover all bases in a final way. You are quoting the word stuff in the sense that you are putting quotation marks around it. Unless you are quoting the question Stuff?, the question mark is obviously not part of the quoted material.

Also, the APA Style Guide is only for dubious cases. Since there was never a typographic tradition of putting large punctuation such as question marks inside the quotation marks when they don't logically belong there, the question doesn't even arise for question marks in the first place and so naturally the APA Style Guide was not written with the intent of settling it. (The tradition of putting periods and commas inside the quotation marks was originally in order to put them closer to an alphabetic letter so as to protect the delicate (physical) letter/type/sort against breaking off. It is only by inertia that some style guides still require it now that the necessity no longer exists. To the extent that there is an optical problem, a thin negative space that could be applied automatically would be a better solution.) It's just an accident that the APA Style Guide can be interpreted so as to yield the correct result.

Since you are writing dialog and not quoting, the rule is simple:

Make it a complete sentence.

If your punctuation in dialog is part of the sentence, therefore it goes inside the quotes.

He asked, "Why should I do this?"
"Where are we going?"
"Let's get out of here!"
He yelled, "I want you to do this now!"
"I don't want to do this," I screamed back. Note the difference here.

Now, if you're characters are quoting other characters, that's when you do it differently:

He asked, "Did she say, 'I need to know' or 'I want to know'?"

As a side note, I've never ever heard of anyone using MLA to write a work of fiction. And novelists often break the rules for narrative purposes.