Which mobs you have to kill is not marked on the nameplates. this should be these three as far as i can tell
https://www.wowhead.com/wotlk/npc=32290/cult-alchemist
https://www.wowhead.com/wotlk/npc=32289/damned-apothecary
https://www.wowhead.com/wotlk/npc=32276/cult-blackguard

questie version: 7.3.0

This should be fixed as of #4411 with 246bbc6.

Looking into this further - the mobs that need to be killed should show up correctly without database corrections, and they do on my client, as they are listed as dropping a requiredItem for the quest (44301).

246bbc6 was an incomplete fix however - I'll finish it off and extend it to the other versions of this quest (horde and alliance both have initial and repeatable/daily versions).