Once you have configured the custom relationship permissions, you will have the ability to give this custom relationship visibility into the employee's private goals they have been set to oversee.
To view this, the person who has been given this visibility and applied this custom relationship can go to the Profile page of the user they now have visibility into. The employee can be found under the "My Team" section of their People navigation.
Here, they can view any Goals (private and public) associated with this employee.
As a reminder, this gives only visibility. The user will not be able to take action (such as delete, edit, or update) a goal.