If you have access to Kik, you can find your username in your profile screen :) Go to your Settings and your username appears in smaller, grey font right under your display name and profile picture.
Can't login to Kik because you forgot your username? No problem, on Kik you can login using the email registered to your account or your username!
If none of the above works for you, check your email for an old confirmation message from us, you'll be able to see your username there.
If you've forgotten your username and email, and don't have access to the confirmation email to find your username, you won't be able to access your account :(