This guide features exactly where you'll need to go to find the hidden "N" letter location when it is released! Collecting these letters will eventually unlock the hidden mystery skin for the Chapter 2: Season 1 battle pass! There's eight weeks in total, so be sure to get them done when you can.
These are pretty much exactly like the battle stars from previous seasons, but instead of gaining stars you will now gain experience. This is a pretty big change because you would gain tiers by earning stars and not experience, but for Chapter 2 it looks like you will only need to obtain xp.
You'll need to complete eight of The Lowdown Challenges to unlock the loading screen that enables you to search for the letter N.
Hidden N Loading Screen
Once you've completed eight of these challenges, you will receive The Lowdown loading screen! This looks to kind of being exploring the lore of the season where each of the cosmetics have an alter ego. The hidden N can be seen on the left side of the image at the back of the hangar.
Hidden N Location
The N is at a location you've probably already visited, because it's at the E.G.O. Hangar. Inside of here you'll want to go to the back of the hangar and up the stairs. The hidden N will be on top of a couple of yellow barrels.