Can anyone tell me what you have to do to get this quest for another heart essence? its not showing up in my chamber of heart but it has on all my other toons
The comment section there should help you figure out where you’re at in the quest chain.
You need to have done the intro to Nazjatar and then started the chamber of hearts quest chain from the capital city.
The main places to check:
Capital city (Dazar’alor for horde)
Chamber of Hearts
Uldulm