On this page of the Far Cry 6 guide, we've listed the locations of all Criptograma Charts available in Isla Santuario. We've described the cards from the Vencejo and Quito subregions.
The first chart can be found in the metal tunnel. Just enter it and you'll see the chart at its very end, on a blue wall.
The next chart can be found on the roof of the building the crate stands by. You must jump onto the roof, move past the car seats and look at the bricks. The charts lies on them.