Originally Posted by
Andyssian
1. Blood And Wine quest chain requires Honored standing with the Nightfallen + completed Waning Crescent storyline.
2. Statecraft quest chain requires 8,000/12,000 Honored/Revered with the Nightfallen + completed Blood And Wine storyline.
3. A Growing Crisis quest chain requires 7,000/12,000 Revered/Exalted with the Nightfallen + completed Statecraft storyline.
4. A Change of Seasons quest chain is currently unknown as it required drops from the Emerald Nightmare raid, which didn't happen on beta and so far it isn't possible to do it on live as there is no way someone has the rep needed to complete A Growing Crisis and the raid hasn't been unlocked yet.
You primarily gain Nightfallen rep from:
1. Completing some (NOT ALL!) normal quests inside Suramar zone, including the quests that unlock Leyline feeds (didn't count how much they give, but from my experience they should bring you pretty close to hitting Honored).
2. Completing world quests in Suramar (usually about 300-400 rep + bonuses per day from my experience).
3. Completing Nightfallen Emissary Quest (1500 rep + bonuses).
4. Feeding Valtrois, Thalyssra and Oculeth Ancient Mana every day (150 rep + bonuses per day).
5. Completing "Withered Army Training" scenario (anywhere up to 425 + bonuses every 3 days).
6. Supposedly you might get Nightfallen Insignia from World Quests (250 rep) or Dalaran Emissary Quest (750 rep).
Aside from the normal quests, all those sources are repeatable.
P.S. Keep in mind that probably due to a bug, some of the World Quest DO NOT appear on your map and you might stumble into them while running around the zone. For example, a "Clear the Skies" world quest in Felsoul Hold might not appear on your map/tracker addon, but if you do to Felsoul Hold for whatever reason, the quest will automatically start and award reputation as normal.