It looks like you have 2 step authentication setup, did you receive a text with a code?
You'll have to go here https://accounts.google.com/ServiceLogin?service=mail&continue=https://mail.google.com/mail/#identifier
enter email --> forgot password *****> don't know password ***** continue --> I don't know --> can't access my phone --> then answer questions
If the account is tied to an old cell phone number this is the only way to try and retrieve it.
Did you answer the 2 questions?
When was the last time you were able to sign in to your Google Account? (Required)
When did you create your Google Account? (Required)
you can sign into the gmail account through your ipad?
we can continue when you get back, there should be a spot to change your password ***** phone number etc. within the app
open up the gmail app and look for the gear switch for settings
is it he general email app and not the gmail app?
shown here there is a gear switch for settings https://itunes.apple.com/us/app/gmail-email-from-google/id422689480?mt=8
ok I just downloaded app, doesn't look like you can change password ***** it
You'll have to contact google support to see what they can do. https://support.google.com/a/answer/1047213?hl=en
you can ask, not sure if they can retrieve an embedded password ***** the ipad or not.