A fast and simple way to find missing assessment results for students is to start by choosing Student Assessment on the Analysis page for your data and breaking that out by By Assessment (or by By Student). The resulting chart will look something like this:

Next, under Student Assessment Result Filters, select Yes under Missing.

You now see only students who have a missing assessment result. In Pivot Table View you can create a table so you can easily see each student and the assessments they’re missing. Set Left to By Student and Left Breakout to By Assessment.