For EYFS assessment how can we see what percentage of children are on track for each of the areas?

You can see this on the EYFS tracker report. Go to;  Reporting > Assessment > EYFS - Summ. (orange tab) > EYFS Tracker.

From here, you can select the academic year you want to record, the Year and Form group/class. You can select all 17 subject by clicking and dragging down in the subject field of the filters. Then select "choose."