In order to configure different public holidays for your employees, you should create different holiday calendars. Go to Configuration → Holidays and choose "Manage" on the calendars list.
For each country, you need to add a new holiday calendar. Then you will be able to assign a calendar to an employee.
The third step is to add new holidays to the calendar. In order to do that, open Configuration → Holidays →choose the proper calendar from the dropdown. You can add holidays one by one or import them from the list suggested by Google.
Check more details here → How to add public holidays?
After adding public holidays to each calendar you are able to assign a calendar to an employee. In order to do that, open Configuration → Employees and edit a chosen employee. In the next step just choose the new holiday calendar from the list.