While exploring Hell, you will run across icons on the ground that look like binoculars. Stepping on one of these will prompt you to either look at something specific or press a button, which will make the character you’re playing as say something about the area or object you’re looking at. These are Commentaries and there’s a total of 60 in the game.
You will be able to find 30 of them while playing as Gat and another 30 when playing as Kinzie, with the locations being the same between both characters. They will appear on your map when you purchase the Collectible Finder once you get to level 15, although the same icon is shared with Audio Tomes.