On this page of our guide to Psychonauts 2 you can view the locations of Half-A-Minds appearing in Tomb of the Sharkophogus.
There is only a single Half-A-Mind in this level.
Location: Tomb of the Sharkophogus.
Half-A-Mind is on the third platform, right behind the gate. You need to look to the right, next to the typewriter.