Thanks for the idea xterra.
I have just worked out one option. Not sure if it would work on my friend's iPad.
On your iPad,
1. Go to Settings
2. Scroll down on the left to the option Passwords
3. Select Passwords.
4. It may ask for your iPad password or fingerprint. Give it to the iPad
5. On the right, it would have all the passwords the iPad knows in the clear. One of them will be for your Gmail account.