You can certainly ask "What did happen last night". However, the meaning changes to one of emphasis. The question asks not only what happened, but in contrast to some earlier discussion where something else was said not to have happened.
In the exasperated "Who does want to eat", it is the same situation: emphasis.
We also need the auxiliary, if the WH-word subject is paired with the verb "do":
- What {did you do | did you*} last night.
The * marked form sounds archaic. This construction probably occurs to avoid a perceived ambiguity: "what did you last night" sounds as if "did" is still auxiliary, and the verb is missing. "What did I what last night? What did I eat? What did I watch on TV? Oh, you're asking me what I did, in some outdated way of speaking; very funny!"
(Some uses of this word order in questions still occur in British English, I think, such as, "Have you the time?" "Had you enough to eat?" Children all over the English speaking world continue to pick up the syntax from nursery rhymes: "Baa baa black sheep, have you any wool?")
Note that since the "did" is required in "what did you do yesterday", it is possible to use it with or without emphasis:
- What { did* | did } you do yesterday? [Emphasis: I already know what you didn't do; please give me the contrasting information: what you did. No emphasis: inform me about your yesterday's activities.]
We can also put the emphasis almost anywhere in the above sentence: we can emphasize "did", "you", "do" or "yesterday", in order to make any of them the focus:
In our earlier sentences, we cannot use "did" without emphasis:
It is possible for another word to be emphasized simultaneously, in some very specific contextual situation where things are being contrasted in parallel pairs, or something of the sort:
- Okay so we established what didn't happen to Joe; so what did happen to Bob? [The focus is on Joe and Bob, and on what did happen to the former and didn't happen to the latter: two things in one sentence contrast pairwise with parallel things in the other.]
Ordinarily you use the 'declarative' only when the question is 'echoic' - that is, when you are asking for confirmation or clarification of what you have just heard, often explicitly echoing the language your interlocutor has employed. In most cases you will stress a specific term which you find incredible or did not hear clearly.
A: Janet's going to France next year!
B: She's going to France?
C: Janet's going to France? I thought it was Jessica.
And in these circumstances, where you are questioning what you have just heard, you will not use the ordinary interrogative form unless you stress such a term—otherwise your interlocutor is apt to respond “Weren’t you listening? Didn’t I just tell you that?”
A: Janet's going to France next year!
B: Is it France she's going to? not Spain?
C: Is it Janet who's going to France, or Jessica?
But if you are not responding to what has been said, if you're just asking for information, you will ordinarily use the interrogative form.
Best Answer
I don't think either of the specific questions you give as examples has a bias towards either a positive or negative answer, because neither can be answered with a simple positive or negative—they’re both ‘open-ended’ questions, conditioned by the what at the end of each. They can be spoken with varying emphasis and intonation, which may commit the speaker to a specific attitude. But that commitment is not a function of the syntactic form; the same attitude may be conveyed by emphasis and intonation in ordinary interrogatives
These, however, may indicate an ‘expected’ answer:
These may express dismay, or excitement, or skepticism or confusion about the addressee's prior assertion of these propositions. And in fact, at least to my mind, what distinguishes questions of this sort from ordinary interrogatives with Subj/Aux inversion is that they are almost always responsive. That is, these questions are not used to initiate a discourse or to introduce a wholly new topic; they have to pick up on something that occurred earlier in the present discourse. Note that each of your examples opens with a conjunction, implying a continuation of something previous. My two examples likewise imply an established topic: