With the most recent version (6.0) of the Facebook Graph API, there are no longer endpoints to find mutual friends between two users or get the friends list of a user.
If I want to find the number of mutual friends of two users on my app, how would I go about doing so? I can get the number of mutual friends who are also using the app (https://developers.facebook.com/docs/graph-api/reference/user/friends/), but what if I want to get the total number of mutual friends?
You can’t do that any more.
https://developers.facebook.com/docs/graph-api/changelog/version3.1#mutual-friends-api:
This has been removed for good, and there is no current replacement.