Answer for Prep for just waxed car.

You have to remove the wax completely. Clay/polish only if you have scratches or other paint imperfections you want to remove or you have a stubborn wax/sealant which won’t come off readily with chemical cleaners.
You can remove some waxes and sealants with pre wax cleaners or isopropyl alcohol with water solution but, some do not remove easily and are designed to resist chemical breakdown. You can contact the wax manufacturer and ask them what the best way is to remove their product, if in doubt.
For best results, paint should be free of imperfections (scratches/marring/etc.) and be completely free of waxes or sealants.