the root is at /private/var/mobile/Containers/Data/Application and then there's a folder with strange UUIDs corresponding to each app. You could install the iVim app and open Terminal using :terminal to view the path, but you won't be able to view other apps' folders using this, so you should try to extract them from your backups instead.

If your backups were made from iTunes and not iCloud and they weren't encrypted (if they were you can try making another right now), then you can try dumping the manifest.db file for the backup which has the names of all the files inside including your CoPay files.