I didn't play the demo, but I'm pretty sure the questions are repeated in the main game. But considering the main game has 73 episodes, and there are two DLC packs out already, I wouldn't worry too much about seeing some of the questions again.
There's no I in TEAM but there's a ME, and there's no I in TEAMWORK but there's an EWOK. Zorak
Yes, I believe the 3 episodes in the demo are in the full game as well. I'm not 100%, but I just got through playing 25 episodes or so and recently came across a duplicate episode from the demo. Stop playing the demo now and get the full game!