Can I Review the Questions I've Played?

YES! As long as the Challenge that you're subscribed to is active, you can check out all the played Questions from the Timeline.

Just look for the green check and/or the red X. It's also identifiable by the header that reads "Question..." #1, 2 and so on. 

And when you click on the box, the played Question opens up again in the app so you can manually revisit the Question sequence by clicking the buttons Clue / Question / Insight. This way you can check out the Questions you got wrong (or right!)

But wait, there's MORE! You can also review any Questions you weren't able to play once the Challenge has ended. Just look for the "Review Unplayed Q's" tab on the timeline once the Challenge has ended.