Which is correct?
Only me is working today?
Only I is working today?
Which of these should I use? Or neither?
You should use "I", but the verb must agree.
Only I am working today.
But other expressions are possible and may be prefered:
I am the only person working today.
I think it would be better to say. I'm the only one working today or I'm working by myself today if you're completely alone.