Hey! Awesome to hear your going on a discovery flight!
You can expect:
•a full run down on the basic functions of the aircraft
•a walk around with the instructor
•you likely will be in the left seat
•If your instructor is comfortable enough they may let you take radio comms
•You may get to taste how taxiing works as the pilot
•You can follow your instructor along on the controls during takeoff and landing (some let you takeoff and land if they are comfortable)
•You will be doing a lot of hand flying while in the air during climb, cruise, and descent
•Basic maneuvers can be expected to get a feel for the aircraft in the air
•You can expect a debrief at the end
As for the quizzing, if you show your instructor you have prior knowledge of aviation, they may throw out some basic questions to see what level you are on. I got quizzed very briefly before my first flight on the basics so my instructor knew I had prior knowledge. Because of this he let me takeoff and land on the first flight. If you have any questions feel free to ask!
There’s no expectations at all for you besides that the instructor expects you will know nothing. With that being said, take it as an opportunity to enjoy the flight. You’ll probably fly for the majority of the time, and most discovery flights have the student perform the takeoff. I’d just say to not hyperfocus on trying to do well because in a discovery flight you should be appreciating the experience and exploring the aircraft to see how it feels.
Use caution. My piece of advice is always “go into it acting like you know nothing”. IRL VFR is nothing like IF. Unless you’ve read the official FAA documents (PHAK, FAR/AIM, etc.), let the instructor teach you things without trying to prove your knowledge. You may already know them, but chances are you’ll learn a lot more by just letting it all happen.
Just have fun! There are no expectations for you. And if it’s your first time in a small plane, it’s entirely possible you may feel nauseous. That’s totally normal though.