This page of the guide to Psychonauts 2 contains all the Supply Chest Keys available in the Questionable Area.
There are 4 Supply Chest Keys in this level.
1st Key
Location: The Forgetful Forest.
You will come across this key by jumping through the trees in the Forgetful Forest.
Reaching it is easy.
You just have to follow the path, i.e.
jump on the branches and bounce off the leaves.
2nd Key
LocationCampgrounds.
This key is on a small platform by a tree.
you’ve got the option to reach it by jumping off the bonfire.
3rd Key
Location: Fierro’s Funicular.
you should probably enter the mist-covered area, near the rocks you will see a glowing key.
4th Key
Location: Sassclops cave.
