I am no expert at writing exam questions, but I'll post these just to give an example of the sort of open-ended questions you might use.
Year 1, Term 3
Tell a story about King Alfred.
Tell about Edmund Ironside and Canute.
How did Harald marry Gyda?
What did Buffalo Bill do that was so amazing?
Name one of the Great Lakes and tell what it looks like.
Explain how a lock works.
Tell all you know about two different birds (cardinal, catbird, rose-breasted grosbeak, scarlet tanager, brown thrasher, mockingbird, thrush, linnet, goldfinch, tree sparrow, junco).
What poor choices did King Lear make? What happened because of them?
How did the cat in Just So Stories manage to be allowed to live in the cave?
Year 4, Term 3
Explain the importance of either John Newton or David Brainerd.
How was the French Revolution different from the American Revolution?
Tell all you can remember about one of the battles of the American Revolution.
How did Abigail Adams affect American history?
Describe in detail two interesting features of the Mississippi river or the areas along the river.
Explain longitude and latitude.
Explain one argument against the idea that life just evolved.
Which planet would you most like to visit? What would you likely find there?
What advice would you give Dion, and how would that advice help him?
Which character in Hamlet was the most responsible for what happened? Why?
Tell the story either of Cupid and Psyche or of Ceyx and Halcyone.