In the Omori game you can obtain a number of keys. These keyboard keys are labeled with a capital letter. The letter keys start with A all the way to Z. You can find the J key here.
Omori Location Key K
You can find the Omori K Key in the art gallery in Sweetheart’s castle.
Looking for Key L. Find the Omori Key L.
You can find all Omori key locations here.