All the Tallnecks are marked on the map from the start except for one. In order to override them you will have to solve a general climbing puzzle.
Since most of them appear on the map you're likely here trying to find the one that doesn't. It's called Salt Bite and can be found in Cauldron: IOTA and will unlock with the completion of it which can be found here:
As for the rest, here is how to climb up to them:
Cinnabar Sands:
The Stillsands:
The Stand of the Sentinels:
Landfall:
The Shining Wastes is an automatic unlock in the story and is unmissable.