Ummm… you are suppose to use it in the room with the bones… on the bones.
From the above posted link (https://www.wowhead.com/news/how-to-enter-old-scholomance-farm-once-removed-transmog-items-333981):
To start unlocking old Scholomance, you must first do a normal run of the MoP-Revamped Scholomance all the way to the final boss, Darkmaster Gandling.
Once you complete the run, you must go to the room that used to be Doctor Theolen Krastinov’s room in the original Scholomance (top center room), and at the top left portion of the room, you will find some bones.
Here’s a video (start at 2:55):
