Where is the nearest intelligent life in the universe?
What have I been repressing all my life?
I think I’d ask what could/should we as a society do to make living on this rock forever peaceful for all mankind. No, change that. I’m going with Powerball. Even if I learned the answer to the first question was as simple as the turn of a screw, I couldn’t get the world to listen to me anyway.
I don’t think I’d really want to know any of the Great Answers. Without the uncertainty, there’s precious little room left for hope and self-determination; what would be the point to life when you’re just a puppet with an inescapable script to follow?
In fact… I’d just as soon learn the answers, and more importantly the questions, as they come naturally. It’s supposed to be a journey, right? This almost feels like cheating.
So I’d walk up to the source, go “So you know everything, huh? Cool. Well, maybe I’ll see ya at the end of time.” And spin around and walk away.
Anyone else not want an answer?
I’m tempted to ask a personal question like “How can I be happy,” but there would surely be some horrible ironic catch like in that story “The Monkey’s Paw”, and after following the advice, I’d end up lobotomized or something, but oh so happy!…
So, I’m wavering between one of the big philosophical questions (“Is there a god?”), a question relating to my personal life (“How can I be confident?”), and something simple and avaricious (“What are next week’s Ontario lottery numbers?”). Because having the opportunity and not asking the question would eat away at my mind forevermore. Jadis of Charn knew that well.
My question would be: “What question should I ask?”
Only one question?
Doh!
I’d go with this as well
Who really killed JonBenet Ramsey?
Heh, we’re like minded. Although close on the tail of that one would be “What should I do with the rest of my life ?”
But more likely, I’d ask the Ultimate Source of Knowledge : “Mind if I hang out here for a while ?” 
Definitely something related to lottery numbers and jackpots. The other Q&A’s I prefer to wrestle with while I sit on my toilet or in the shower.
Quickly: if you had this opportunity to ask an all knowing source of info, wouldn’t the existence of this all knowing source already limit the possibility of “one god”?
Probably want to also toss in something like “…and what’s the answer to that question?”.
You won’t like the answer.
I would refuse to ask a question, just to piss off and confuse this source of infinite knowledge.
What is the true nature of quantum physics?
What makes a woman tick?
Was it really her and not me? Fortunately, I’ve only heard that line once. 
Seriously, though, I’d go with with a scientific question. Give me the Theory of Everything. That’s something that I don’t need to worry about people thinking I’m nuts over. I publish what said entity tells me and sit back. I may look like a nut at first, but in the end, it’ll match up with all our observations and people will say, “That Drew sure was one smart fella’!”
Which question I choose is going to depend on how selfish I feel at the time.
If I’m feeling selfish, “What if anything can I do to start healing the rift between my siblings and me?” And if the answer is “nothing”, I’ll cry for a week, but I think I’m still better off knowing.
If I decide to use this opportunity for the Good of Humanity, however: “What energy sources are worth using time, money and brain power on?” Because I firmly believe that every plan to reduce environmental pollution and to raise people out of absolute poverty has got to come down to using this wonderful thing called crude oil more wisely, which means among other things burning a hell of a lot less. That in turn means both using less energy and finding other ways to get the energy we need. I think the second is more of a challenge at the moment.
Answer: NO
Reason (unspoken): You’ll be unhappy because you’ve been told you’ll be unhappy, this knowledge makes you unhappy.
Yeah, I’d probably have to go with the lottery numbers, too – the answer to any other even remotely meaningful question, I’d likely be unable to understand.