What is the chemical formula of coffe?

Coffee is not a chemical compound but a brew so it does not have a formula. If you meant to ask about the formula of caffeine I can give you the emperical formula: C8H10N4O2
It's based on Xanthine which has 4 hydrogen atoms, 3 of them are bonded to nitrogen atoms. In caffeine these three hydrogen atoms are replaced by three CH3 groups also known as methyl groups.
Xanthine is aslo a purine