You can get to this report using the navigation bar.
The graph shows the total number of alerts triggered by each employee and the alert type as a pie chart. This allows you to see which employees are triggering the most alerts and to take further action if necessary. Currently this report only works for the built-in reports.
You can filter the data by selecting a start date and end date or choosing one of the displayed date frequencies (e.g. last 7 days) using the calendar buttons displayed on-screen to quickly find the information you are looking for.