This is an unmarked quest from Jobsworth Bones in the Employee Lounge, which is in the Pit of Bureaucracy.
He asks you to play a game where you select one of the skulls on his belt.
You want to touch the one that's not poisoned.
The middle one is the one that is not poisoned
Your rank will be reduced by one and you will receive the Red Key which is used to get into the inner bureau.