Just click on view HTML and see, in the code, where that popup is being displayed. If you found it but the code is somehow obfuscated, then most likely your website is hacked.
If you can't find it, then do a grep (if you have access to a VPS) at the root level of your Joomla website:
grep -R "We Ready"
If the grep didn't return any results, then try searching the database (the whole database) in phpMyAdmin.
If that still didn't work for you, then try switching to a different template to see if the problem persists. If the problem is gone, then it's the template, and the code is obfuscated there.