Can you apply the epoxy over an oil based stain on wood?

The answer would be no. Epoxy can go over water-based paints because they dry fast. Oil-based paints, on the other hand, take longer to dry completely. Before applying a seal coat of epoxy, if an oil-based paint is used you must use three coats of oil-based polyurethane to seal the surface. This is a crucial step in order not to run the risk of the epoxy sticking to the surface and or peeling off months later.