Feed Thalyssra

There are 3 quests in Shal'aran Suramar (Cave at 35.0, 47.6). All of them work like daily quests. You feed NPC with 50 [currency=1155] and he gives you a buff and 50 reputation with the [faction=1859]. Can buy buff at any time, but reputation quest can be done once in 24 hours.

You can see red bar. https://i.gyazo.com/160c4be41b1f6c6f1bd3bcc352e89ac4.png
It shows how long you have to wait till the next time you can feed the npc.

You can't interact with npc if they need food, so feed them if you want to complete quest or start a new one.

Quest

NPC

Buff

Quest Video

Feed Thalyssra

[npc=98312]

[spell=224772]

https://www.youtube.com/watch?v=IPxl774t8yE

Feed Valtrois

[npc=112145]

[spell=224189]

https://www.youtube.com/watch?v=eDIEc9A4R-E

Feed Oculeth

[npc=102017]

[spell=224186]

https://www.youtube.com/watch?v=5mI-O1aEObs

You need to progress in Suramar storyline to get npc in Shal'aran.

You can see full quest chain here: Nightfallen But Not Forgotten.
Feed Thalyssra available after Shal'Aran
Feed Valtrois available after Feeding Shal'Aran (not sure)
Feed Oculeth available after Arcane Thirst

Buffs demo:
[spell=224189] https://www.youtube.com/watch?v=hLSMqaku25w

Thalyssra is actually a She, but otherwise good info. :)

It should be obvious but once you cure Thalyssra/Valtrois/Oculeth you will no longer get this quest.