How to check my iOS-backup password
If you saved it in keychain, it will auto-fill in the Change Password dialog.
If so, it's listed in keychain as &quot;iOS Backup&quot;, where you can open the plaintext version to see.

If not, then I think you'll have to try changing it to see if you remembered it correctly. I don't know if it will allow changing to the same password - never tested that.