You only get to Holmes after you beat all 5 Game Shows, then avoid his robots to reach the sewer entrance on Main Street. Beat 4 of his security systems, and you can use the Inventor's thumb drive to reprogram Holmes to be friendly again.
(see related question)
He is in the vent by the drink station in the club
the code is 2014 but the way you find out is that you use your heat goggles
You have to beat all 5 game shows, then return to Main Street to find Holmes. Except for the Tokyo game, you are returned to the street to take your jet to the next place. On Mr. Yoshi's show, click the background after you have won the show. (see related question)
You only find Holmes after you beat all of the game shows. Return to Main Street and the Inventor will tell you to come down the sewer. Go right across the building and then jump down. The Inventor will give you some code to repair Holmes' programming, but you have to go through several "code circuit" challenges to reach his central processor.
Beat all 5 of the game shows, then return to find Holmes in his subterranean hideout. Solve his circuit diagrams and reprogram him to be friendly to humans again. (see related solution question)
When you complete all the game shows Holmes will tell all the robots to look for you. You walk into town and run to the manhole and jump down where you will find the inventor guy waiting.
find him
the inventer gives it to you
There is no AC, you have to go to the factory.
After you find him in the attic he is on the roof of the nightclub. Hope that answers your question. :)
On Game Show Island, you don't need to find it in order to complete the quest.
it leads to the door on the outside of the club