The note is found in Wavy Willard's Water Park. It is on top of a cabinet in the mechanical room of the wave pool.
Hey, guess who Supervisor Jenkins picked to clean the toilets again? If you guessed it was you, then ding, ding, ding - you win a prize!
Oh, and it's Chili Cookoff Week, so you better stock up on cleaning chemicals. I put a whole bunch of them in the utility tunnel under the entrance to Crocolossus Mountain.