Hi, I'm Jamie.
Sorry to hear that you're having trouble with this but I'll do my best to help.
It should show the email associated with the account at the login page. Not necessarily an msn email.
Go to another computer and go here to retrieve it.
He has windows 10 correct?
he doesn't have access to the email that's showing on the login screen?
On his computer it doesn't show an email address below the user name at his login screen?
Glad you got it fixed.