If you have created locations outside of either 'England & Whales', you can add public holidays which will be shown in the Holiday/Attendance chart.
Note: You can check the locations that have been created via
Setup & Admin > Locations.
To add public holidays, navigate to
Setup & Admin > International statutory holidays.
Here you will see a list of countries you've created locations in.
Pressing 'Edit' on a location will allow you to add public holidays for it.
Note: You are unable to add public holidays for 'England & Whales'.