You can add this as a field in both notifications and certifications.
To add the course score to a notification, you will need to go in as Administrator to the Events Engine and add a notification (1).
The course average score tab (2) is available for the following events:
1. On course completion
2. X hours after course completion
3. On course failure
4. On course expiration
5. X hours before course expiration
6. On certification acquisition
7. On certification expiration
8 X hours before course expiration
The same data can be shown in certificates by going as an Administrator to Account and Settings, Certifications and then clicking to edit the template of the certificate (3).