Question: can jotunn drop from any forge?
Answer: There are no Exotic quests that reward Jotunn and it will not drop randomly from an Exotic Engram or be sold by Xur. While Le Monarque can be earned from any of the four forges, Jotunn is only available through Bergusia, the final forge. Jotunn has a chance to drop when forging weapon frames a the Bergusia forge.