Why do I get jealous over a girl even though I don't want to be with her at all?

 Both "who cares?" and "who does care?" are grammatically correct.

"Who cares?" is a rhetorical question that is used to express that the speaker does not care about something. It can also be used to challenge someone else's opinion or concern.

"Who does care?" is a more emphatic version of "who cares?" It is used to emphasize the speaker's lack of interest or concern.

Which phrase you use depends on the context and the desired effect. If you are simply expressing your lack of interest, then "who cares?" is sufficient. If you want to be more emphatic, then you can use "who does care?"

Here are some examples of how to use each phrase in a sentence:

Who cares what they think?

I don't care if it rains; who cares?

The politician's empty promises made me wonder: who does care?

I'm not going to waste my time on this; who does care?

I hope this helps!