Does “Who knows” need a question mark?
On the Web, the majority seems to think we need a question mark in the following context:
Q: “What is the meaning of life?”
A: “Who knows?”
I disagree. I consider “who knows” as a phrase or an expression, not a question; not even a rhetorical question. Adding a question mark sort of ruins the response especially in writing because it sets up an expectation (or subtle tension) of further response. A period, I feel, is the right choice because it’s a complete answer. In speech, we would not pronunce “Who knows” as if we are really asking a question; that is, our tone is missing the question mark. What do you think?