Look in the section titled "Factory Settings," "PIN Code," or "Wireless Connection." QFX typically hides it in the troubleshooting appendix.
The answer seems trivial: there is no password. Or more precisely, the default credentials are: qfx default password
Every engineer who unboxes a QFX, performs a zeroize, or loads factory-default configuration must immediately set a strong root password or—preferably—disable root login entirely. Document the change, verify it, and include it in your configuration management database. Look in the section titled "Factory Settings," "PIN
Type recovery at the prompt to start the password recovery process. " "PIN Code