Use an open end wrench that fits, place a towel and pry off. Need to place equal pressureabove and below and on as much of the knob surface as possible.

I would try rapping the knob (depending on knob cond.) with a solid item to maybe loosen up/crack varnish or gum that is holding it on there.

I would also consider that the previous owner used epoxy or super glue to attach the knob. There is a small metal D shaped ring that if missing, is hard to replace. Glue is the ultimate solution.