Searching how many days an employee was sick goes as follows.
Choose in the menu for Schedule - Absence & Availability.
If you're in calender view, go to list view.
3. When 'requested' is still checked under status, the list will only show the requested leaves. You can show everything by clicking the X.
4. Select the date for e.g. an entire year and filter (button on the left) for 'Holiday type' - 'Sickness' (= ziekte).