This guide features exactly where you'll need to go to find Fortnite's hidden "I" letter location! You'll want to grab all of these hidden letters to unlock the mystery skin for the season.
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 Hunter And The Hunted Challenges to unlock the loading screen that enables you to search for the letter I.
Hidden I Loading Screen
Once you've completed eight of these challenges, you will receive Hunter And The Hunted loading screen! We get introduced to more of the story in these, it looks like the alter egos of the skins are up to no good. The most important thing is that Rippley looks cute trying to eat an apple in quiet. To find the letter, look to the center of the image towards the top.
The I location is on the third tier of the big barn at the north portion of Frenzy Farm. Run up the stairs and you'll see it near the window that's facing the front of the barn.