No question suffices by itself. Proof: suppose there were some question that allows you to determine which path leads to Utopia, even if you happen to be talking to Bill Gates. Then there would be a range of responses that would lead you to pick the left path, and another range that would lead you to the right. But Bill, knowing your expectations and being as perfect a logician as you, would say whatever it takes to lead you astray (i.e., to Microsoft).
Solution: the problem said you only get one question. It didn't say that you can't rip the box off the person's head first. If it's Bill, you're screwed: you might as well guess. Otherwise, the standard rec.puzzles method applies ('which path would your opposite tell me to take?'

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Jim Ferry Center for Simulation