What is the largest breaker I can take off a 200 amp main residential panel to a shop?

Usually 100 or 125 amp. It will say on the label inside the door.

Check the specs for the panelboard with the manufacturer of the panel. In spec for the panel they will tell you what the largest breaker is.

For example the new 84 slot /225Amp panelboards from Square D, show the largest breaker as 200Amp.