The patch notes say that the warden class skill books have been added. This means they RNG anywhere in the world.

There was a time when the skill books were set, like sky shards. When the game first came out you could use a map to find a specific skill book in a specific location. But sometime in 2015 they RNG'd it. The shelves that at one time contained a smith book can now draw any skill point book. And as you learn more, any given shelf has a lower chance to drop one you need.

But the warden books should drop from anywhere in the world.