If you already finished all the quests in Uldum and still got some until you get the achievement for this area (Unearthing Uldum), then you have to know some quests, even chained are hidden, secret.
For example there is a quest that drops from Myzerian, is the big red dragon that has 20% hp left and is roaming an area you already cleared with the Harrison Jones quests, after you solo it, it will drop the “head of Myzerian”, and it will be rewarded with some jewels and a quest done.
Besides this, there is also on the area zone of Halls of Origination, on the steps there a hidden quest, that drops from a mob there. And is chained, resulting in 4-5 quest, the last one being really really fun, you have to ride a fire ball and all the little pygmies are getting stickied to it.
These are the only secret quests I’ve found so far, still missing some, the last ones maybe they drop from a certain mob.
Update.
There is a quest that does not appear on the map after you take it gived by Salhet the tactician.
The quest is fun, you are about to control some lions in a fight vs hyenas.
This isn’t marked on the map and many players have missed it, however it leads to a chainquest.
Where is Salhet the tactician?
The npc is located south of Akhenet fields on the mountain. Go up and you will find it.