The "Requires Marking" drilldown displays the number of learners whose work needs to be marked. If you click on this card, you'll be shown the pieces of evidence that require marking for those learners.
Please note that if a learner has more than one piece of evidence to be marked, the "Requires Attention" card will only display one per learner, meaning there could be additional items that require marking.
When viewing the Drilldown, you have the option to sort by the Learner's name, to see the records grouped accordingly.