Can I bake bread in a cast iron Dutch oven with the lid on, or should I use tin foil instead?
Presuming the Cuisinart knob is made of the same material as the Le Creuset one (Phenolic), the given maximum temperature is 375°F.

However, many people (including this thorough article) recommend covering it with foil to protect it at higher temperatures. Also, I would suspect that giving 375°F as the limit means that it's OK to go higher, just not too often, and also they won't guarantee it above that temperature.