How do I determine Child Support if I don't know how much the child support provider makes?

Yoiu don't indicate where you are in the court process, but the system is set up to require each party to submit a "Financial Disclosure Form" -- with back-up documentation -- showing income from which support is determined.  If you are not in court, ask for salary/wage information informally; if you can't get cooperation, file a motion.  For information on how child support is determined, and the current presumptive maximums and other information, see here.