All (heh) of this discussion reminds me of the many times we have talked about longings for words that indicate various nuances of meaning; the thread about one to distinguish a homosexual marriage is the most recent one that comes to mind. Helen, Anna and Faldage were right: your second and third examples have a different meaning from mine. At least here, they would. I read yours as meaning the plural sense of 'you', whereas mine were purposefully singular.

Though you-all (emphasis on the you, hi mav :-) ) is not standard grammar by any means, I do like being able to have my listeners (em, well, 'round these parts, anyway) know for a fact that I'm meaning a singular or plural you, just as I know their meaning. Come to think of it, I reckon I'm lucky to live in this fairly narrow band of North-Southness; not too much further south from here, y'all is also used in the singular sense. But not here, and I'm glad. If I were intending to find out, say, every stop the group made on their trip, I'd say, "Where all did you-all go". However, that grates a bit even on my Southern-fried ears; normally I would hope that context would allow me to just say 'you' and the listener would know I meant the group.
But yes, Faldage, you were right when you said The emphasis is on the list . Dody, I've never heard anybody put the 'at' in there, but I suspect your examples mean the same as mine. If your class had had a party and you hadn't gone, the next day you might ask a classmate, "Who at all was there?". If you meant that you wanted your friend to tell you the name of each person that attended, then yes, that would be the same as me asking, "Who all was there?"