During the night, there are choppers that take you above the canopy. Take the chopper in the south-east (bottom right) corner of the map. After that boss fight, you can easily glide there using updrafts and speed.
With regards to your last POI, zoom out so all of Verdant Brink fits on your screen. Now, in the top left corner, hover of your POIs a few times. You'll see the unfound ones blink on your map.