Select the assignment and click Analytics in the menu on the left.
Click Rank correlation. The Rank correlation page is shown and a couple of insights are given:
How well each question has been answered by the percentile students that got the worst grade for the assignment, until the best percentile.
It shows graphs. If the line in the graph is about horizontal, it means the question was equally good answered by the best-graded students as for the worst grade students. If the line is more inclined, it means the best-graded students answered this question better than the worst grade students, as you would expect for most questions.