What is the best way to get dried wax off of a plate?

Take plate outside, wear rubber gloves and pour boiling (or almost-boiling if you fear that the plate may crack) water over it.

You can buy little gadgets called Bobeches for just that purpose.

Razor blade…...

All you have to do is run hot water over it and the wax will melt off. :)

On a plate any of the above suggestions should work. It the wax is on a wood surface use a credit card to scrape it so the wood is not damaged.

I use candle bobeches on my tapers to prevent dripping onto the table and they work great.

Just heat the plate.

Or, alternatively, run an ice cube over the plate briefly to make the wax brittle,
pry it off with the edge of a butter knife, then wash it in hot water & soap.