FCP has about 72 fonts inside the app bundle (there may be more by now). Right click on the App and Show Package Contents. Then navigate:
Contents > Frameworks > Flexo.framework > Versions > A > Resources > Fonts.
To make these fonts available to other applications, select all, and drag/drop them in another location on your hard drive (they should not move out of your app contents — they should just copy/paste to the drop location — **make sure they are not moved out of the app!!!**). You can then install them with Font Book for use for all apps.
Once installed in Font Book, I believe the copies can be deleted, but I generally tend to keep them as backups.