Retrieving password for non working email address that is attached to an iCloud account
While I can assume that you ask due to having forgotten the password, it is not clear from your question.

In case you still know the password, you can log on to the iCloud account at appleid.apple.com, change the e-mail address and make it the primary e-mail address.

NOTE: Obviously, you cannot use an e-mail address you already associated with an Apple ID in a different account.