Magister Alminas:
To get the Resonance Amulet, there are two ways.
One way is to defeat the Demon Halisha, who is located within the Four Sepulchers. you must form a party to enter. If that proves too difficult, defeat the followers of Halisha at the Shrine of Loyalty. By doing so, you can earn "tickets." Once you have acquired over 700 tickets, Halisha himself will appear. By the way, the creatures you must face are the Grave Scarab, Scavenger Scarab, Grave Ant, Scavenger Ant, Shrine Knight and Stander.