Hunting is a great way to earn some cash in Red Dead Redemption 2. If you down game with the pelts in good condition, they'll fetch a high price at the Trapper where you can sell all your animal-related goods.
Tracking down high-level and rare animals, as well as perfecting your skills with the bow may be time intensive, but more frequently found beasts will also earn you good money. Of course, to turn that carcass into currency you'll need to find a trapper. So here are all locations.
Starting from Chapter 2 you'll have access to four Trapper locations where you can sell off your hunting goods while the story missions last, and a fifth is added during the epilogue that isn't accessible beforehand. Aside from one location that's in Saint Denis, all Trapper locations are out in the wild, which is where you'll likely be hunting, so you don't need to worry about a lot of travel.
The first Trapper location is the one in Saint Denis as mentioned above. You'll find the store near a large brick wall painted with a mural that's advertising biscuits. You'll likely spot the hides laid out on the stand from a distance. Look for this location in the market area.
The New Hanover Trapper location is between the Elysian Pool and the state border, in Roanoke Ridge Woods. The Trapper's camp is well hidden in the woods so finding it may not be the easiest task. There are great hunting grounds all around though, so if you're there you may as well make the most of it.
West Elizabeth has two Trapper locations. One is in the eastern end of Big Valley, just a lick northeast of Riggs Station, meaning traveling here is pretty easy. There's deer territory just north of this Trapper location making it a good strategic point for hunting.
The second West Elizabeth Trapper location just may be the best one in terms of hunting. Located way north in Big Valley at the absolute edge of the game map, this location is almost precisely in line with the "Big Valley" caption on your map screen, just at the westernmost point on the border.
You'll unlock the fifth Trapper location once you've completed the storyline, thus unlocking the partial Red Dead Redemption map hidden in the game. This Trapper is camping southwest of Manzanita Post, right below the "S" in the Tall Trees caption on your map.