To enable Make Copy function for entities, the Auto-Generated Number must first be enabled for the record types.
To enable auto-generated numbers:
1. Navigate to Setup > Company > Auto-Generated Numbers.
2. Under Entities tab, mark the Enable checkbox corresponding to the record type for which you want to use Make Copy (e.g. Customer).
3. Click Save.
To test, edit a customer record (or any entity for which Auto-Generated Number is enabled) and see Make Copy under Actions drop-down button.