This is a great topic!
If you need this as an answer, think in terms of the topics you might have studied so far about the Middle Ages.
My favourites are:
- Feudalism (societal structures)
- the Black Death
- the Crusades
- Crime and Punishment
- the Church
- Artisans' Guilds
You could begin with "when" questions. (Like, "When [in what era] was the punishment for robbery a day or night in the stocks?" or "When [in what era] did the Black Death occur?")
You might also make your questions a little more "smart" sounding by combining a few of the topics and asking what they have in common, like "What do knights, barons, serfs, archbishops, cathedrals and pottage have in common?"