The track is about 22 kilometers long so you can imagine that it has a handful of great spots to go and watch the cars. However there is not 1 spot where you can see the cars for very long, like a spotter tower.
The Sabine-Schmitz corner is a big braking zone with a lot of action and is in walkable distance from Apex Nürburg.
The Brünnchen corner is very accessible as you can literally park next to the track fence and watch what spectators also call the YouTube-corner.
If you’d like to get to Adenauer Forst you’re in for a relatively long walk, but it’s worth it. Park your car at the bottom of this street and walk up.