If you don't know your email, you can find that out by going through the steps to reset your password.
A password can be reset at any time by clicking on the blue 'forgot' link right on the
login page:
Doing so will ask you for the e-mail address your account is listed under, and entering that information will get a password reset e-mail sent to that address:
Clicking on that link will take you to a screen where you can set your new password, and an email will then be sent confirming the change, and listing the username associated with that account: