To see your account information such as login email, subscription status, the currently active plan, or the storage space used, tap the hamburger menu at the bottom left corner and then select the Account menu.
On macOS you can find this menu in File > Account.
Why have I this odd @privaterelay.appleid.com email address?
The account you are using is linked to an anonymous Apple email address created automatically for you by Apple when you signed in with Apple. For more info check this page https://support.apple.com/HT210318
I'm no longer logged in and I don't remember the email address I used
Please check your email inbox looking for an email with the subject “Welcome to Moleskine Journey”, this email has been sent to you when you registered for the service, check the email bottom lines, it should report your sign-in email address.
You can check your account status in the side menu, by opening the “Account” menu, or, if you subscribed through the App Store, using the Apple page for subscription management.
How to unsubscribe
You can manage your subscription from the "Account" menu. From there you can tap the "Cancel subscription" button.
Alternatively, you can check the subscription status of the app using the Apple page for subscription management.
If you unsubscribed before the free trial period ends you’ll not be charged (on iOS cancel at least 24h before the end of the trial as Apple advises to be sure to not be charged).