Once you have configured the custom relationship permissions, you will have the ability to give this custom relationship visibility into manager-level custom attributes that you have set up previously.
To view this, the person who has been given this visibility and applied this custom relationship can go to the Profile of the user they now have visibility into. They can find the profile from the "My Team" section of the People navigation alongside direct reports.
From here, they will be able to navigate to the "About" section on the right of the Profile overview, then "Show more about ___" and view that custom attribute, as shown below!

