Go to Muriel in ThaisSorcerer guild here.
Ask him about a quest. He will give you an Ectoplasm Container for you to dig a well-preserved human body in the dungeon north on Thais in the so-called Cursed Bone Pit.
Follow the maps to the Cursed Bone Pit.
Clear the floor from the bodies and dig until you find a humanoid. Use the ectoplasm container on it to receive an Ectoplasm Container (Bone).
Player: hi Muriel: Welcome back, Player! Player: mission Muriel: Indeed, there is something you can do for me. You must know I am researching for a new spell against the undead. ... Muriel: To achieve that I need a desecrated bone. There is a cursed bone pit somewhere in the dungeons north of Thais where the dead never rest. ... Muriel: Find that pit, dig for a well-preserved human skeleton and conserve a sample in a special container which you receive from me. Are you going to help me? Player: yes Muriel: Great! Here is the container for the bone. Once, I used it to collect ectoplasma of ghosts, but it will work here as well. ... Muriel: If you lose it, you can buy a new one from the explorer's society in Northport or Port Hope. Ask me about the mission when you come back. Player: bye Muriel: Farewell.
Player: hi Muriel: Welcome back, Player! Player: mission Muriel: Excellent! Now I can try to put my theoretical thoughts into practice and find a cure for the symptoms of undead. Here, take this for your efforts. Player: bye Muriel: Farewell.