How to Find my email ???

The Apple ID is not signed in the device ( iPhone ) , you didn't own the phone number and device so Apple ID will act as a simple mail address .

You need account credentials that were set like three answers for respective questions , date of birth , rescue mail address and its password to reset the Apple ID password use this link https://iforgot.apple.com/appleid#!&section=appleid using a web browser .

A green check mark will appear when correct credentials are entered , the account is verified .

See If you forgot your Apple ID password - Apple Support

Note : your emails can be found by signing in with account credentials at www.icloud.com using a web browser Search, filter and flag email in Mail on iCloud.com - Apple Support

Set up iCloud Mail on all your devices - Apple Support