What does a typical discovery flight consist of?
A typical discovery flight is about a 30 minute on the ground introduction to the airplane and the cockpit controls, followed by a sightseeing flight of 30-minutes to one-hour.  The entire process typically lasts 1 to 2 hours.

During the flight, the instructor will have the controls for takeoff, navigation and landing, but may turn the controls over to the passenger for some gentle, easy maneuvers.

You can expect to ask numerous questions and have them answered, but you won't learn a whole lot about actual flying in a short session.

I would advise you to keep your questions to the flight training process, rather than specifics about flying that need more detailed explanations.

Some good questions may be:

How much ground school does it take to get a license?
How much flight time does it take to get a license?
What are some important milestones along the way to getting a license?
Will I have the same instructor throughout my training?
What supplies do I need for training? How much should I expect to spend?