Remnant II - All Archetypes

Archetypes are considered classes in Remnant 2. You can equip up to max 2 classes (the second slot gets unlocked after you level up your first class up to level 10). To get other classes, speak with Wallace in Ward 13 and exchange special item + scrap and some Luminite crystals for a class item. Equip it in the archetype slot in character tab under invetory menu to use it.

Regular Archetypes

• Challenger - Buy Old Metal Tool from Reggie in Ward 13 and exchange that for the class item
• Explorer - After you defeat the final boss you will get Broken Compass, exchange that for the class item
• Hunter - Buy War Medal from Brabas in Ward 13 and exchange that for the class item
• Medic - Buy Medic Pin from Dr. Noah in Ward 13 and exchange that for the class item

Secret Archetypes

For finding the secret archetype items you can refer to my collectibles guides in the main areas where you can search for the item you need.

• Alchemist - In Morrow Perish area in Losomn, stand next to the sewer gates. Usually couple of these can be found in the area. When you get close and wait a bit, sometimes an enemy will grab you. Defeat Albino Bone Collector and loot Mysterious Stone, then exchange that for the class item
• Engineer - It appears in either the Timeless Horizon or The Eon Vault area in N'Erud (it has to be the second open area there). To me the item that needs to spawn appeared when I had the 3 seeker keys main story fraction. You need to find an edge where you see a cliff on the left, a path in the middle, and some spikes on the right. You can jump there, then down and find Alien Device there. 
• Gunslinger - Listen to all of Moototh's stories in Ward 13 (you can hear the last batch after clearing all 4 worlds and unlocking Root Earth after next story events) to get Worn Cylinder and exchange that for the class item
• Invader - Defeat hidden mini-boss Bane in Corrupted Harbor area in Root Nexus. One of the doors leads to a sleeping corpse (the doors on the right when you enter the area where you get Wayfarer trait in horde fight). Swing with Dreamcatcher melee weapon to get the orb, use the orb from your inventory (or assing for a quick use and use from there if the game doesn't allow you to use it from the inventory). You will be teleported to the dream world where you can kill Bane to get the Wooden Shiv, needed to get this class.
• Summoner - Find Blood Moon Altar (usually spawns where you fight Root Nexus in Yaesha) and exchange 15 Blood Moon Essence for Faded Grimoire item. To get the essence you need to farm purple/pink spirit enemies that appears during the Blood Moon event. To easily trigger it, you can defeat Ravager world boss in a way that you kill the Doe when you are prompted to do so - afterwards, you can farm the spirits in any open area (just shoot them to get 1). Exchange Faded Grimoire for the class item

Getting the last secret Archon Archetype

The toughest one to get. You will need couple of items, equip them and reach the corrupted doors in The Labyrinth. You will glow red like the doors, and only then you can open the doors like you did with the other yellow doors.

• Realmwalker armor set - To get it, if you don't get it with the starting class; finish the game, buy Explorer archetype from Wallace in Ward 13 and then it will appear in Whisper's armor shop. Buy all of the parts.
• Get Explorer Archetype, equip, max to level 10, switch the skill to Golden Compass
• Get Invader Archetype, level up to level 4, and swith to Fortune Hunter skill
• For Long Gun, you need Ford's Scattergun. It can be found From the The Red Throne in Yaesha, the first room on the left. Equip Seal of the Empress amulet and enter the room, the floor underneath you will open, revealing a basement with the weapon inside. Seal of the Empress amulet is a reward from The Eternal Empress if you finish the main quest and being polite in the final encounter with her. 
• For Hand Gun, equip Cube Gun, which can be crafted by McCabe after defeating the Labyrinth Sentinel main story boss in The Labyrinth
• For Melee Weapon, find the Labyrinth Staff. If you follow the path across the locked doors near the first checkpoint where the teleport that switch locations is, you will get to the area where you can fight Bastion Elite.
• For Amulet, you need Leto's Amulet. It can be bought from Reggie in Ward 13, but you can buy it after performing 100 flop dodges. Equip something heavy, and just dodge to flop (ground pound) 100 times. Then talk to Reggie and buy this from him. This is the best amulet in the game, it lowers the load almost in half
• Ring #1 - Amber Moonstone. Can be purchased from Cass in Ward 13. She rotates her inventory from time to time, so keep trying as you play.
• Ring #2 - Black Cat Band. Can be bought from Reggie in Ward 13. You need to die a certain amount of times for the ring to appear in the shop.
• Ring #3 - Anastasija's Inspiration. Can be bought from Whispers in Ward 13.
• Ring #4 - Zania's Malice. Can be found in the Ashen Wasteland area of Root Earth. It's before you find the Resonating Heart Relic; there is a small hole on the other side of the wall, crouch through there.

With all that in your hands, equip it and get to the corrupted doors in Labyrinth. Unlock the doors and enter, you have limited time to find 3 items here, but you can retry if you fail - Strange Box (needed for the archetype), Bisected Ring, and Gunfire Security Lanyard amulet.