This trophy is for listening everything the Master Necromancer Ordan says in Act V.
Ordan is one of the class specific NPCs that can appear in the Pandemonium Fortress. In this case, you need to be a Necromancer for him to appear. You'll see him shortly after entering the fortress and can speak to him shortly after that. Finally you can find him in the second area as well. Each time you'll want to interact with him and select all dialogue choices until they are all greyed out. Assuming you did it correctly, you should get the trophy and challenge complete after the second set of dialogue choices.
This trophy can be a bit buggy in multiplayer in the sense that he may fail to appear at key points. For me personally, I could speak to him and exhaust his dialogue in level 1 and 2, but the initial automatic dialogue that occurs when you enter the fortress did not happen. Returning to the first area in single player triggered the dialogue and at that point I got the challenge and trophy.