For me no question mark just a period when it is a statement. Why does everybody hate so and so? Who knows. (Goodness knows ... I've no idea ... .) Maybe even an exclamation mark.
On the other hand:
Listen up class, if I have x amount of this add x amount of that, subtract x amount of the other and divide it by 3, what number do I end up with. Who knows? (Does anyone know the answer?)
Does “Who knows” need a question mark?
For me no question mark just a period when it is a statement. Why does everybody hate so and so? Who knows. (Goodness knows ... I've no idea ... .) Maybe even an exclamation mark.
On the other hand:
Listen up class, if I have x amount of this add x amount of that, subtract x amount of the other and divide it by 3, what number do I end up with. Who knows? (Does anyone know the answer?)
Just my opinion!