What the achievement asks
Complete a hundred different world quests across Kul Tiras and Zandalar. Ten points, account-wide, both factions.
The word doing the work is different. Repeating the same world quest a hundred times counts once. You need a hundred distinct ones, which is why this takes weeks rather than an evening.
World quests have to be unlocked first
Nothing appears on the map until your character has finished the Battle for Azeroth campaign for its faction and reached the point where world quests switch on for the continent.
A character brought to Kul Tiras or Zandalar without doing that campaign will see an empty map and no amount of flying around will change it. If there is no world quest anywhere on either continent, this is why.
Both continents count
The achievement says Kul Tiras and Zandalar, and it means either. You are not restricted to your own faction's continent: whichever side you play, the world quests of all six zones count towards the same hundred.
That matters, because it roughly doubles the pool of distinct quests available on any given day and makes the hundred come in half the time.
It arrives on its own
There is no efficient route here and no reason to build one. A hundred different quests is a matter of showing up: take everything on the board that you have not done before, ignore repeats, and let the count run.
Almost every other Battle for Azeroth achievement that needs daily attention is doing the same circuit:
- Nazjatarget Eliminated and Puzzle Performer are both gated on which world quests are active.
- Subaquatic Support wants thirty Nazjatar dailies.
- A Fistful of Manapearls is paid for by the same work.
Check the map each day, take what is new, and this one finishes behind the others without ever being the reason you logged in.