[tgrass]

To filter for those managers who will never be happy with anyone's work ask: "Who is your favorite employee? Why? How do you motivate them?"

[jerryr]

I like the intent of this, but I'm not sure I'd ask "who", specifically. I personally would not feel comfortable answering that part of the question. Instead maybe, "How do you motivate your favorite employee?" If the answer is vague or too broad, the manager probably hasn't identified a favorite employee.