The Teachings of Gold are about to become an extremely important resource in Genshin Impact, as two of the upcoming characters that will be added to the game in update 1.1 will need them to level up their talents and abilities.
You can farm the Teachings of Gold at the Taishan Mansion Abyssal Domain. If it is your first time visiting this Abyssal Domain, then you will need to go through the process of unlocking it, as the entrance is submerged in water. As the Abyssal Domains have rotating rewards, you can only farm them on the following days:
The Taishan Mansion is a Pyro based challenge called the Domain of Mastery: Altar of Flames, and it is recommended that you have Hydro, Cryo, and Electro characters in your party when you take on the challenge.
The minimum party recommendation is Level 38, and the maximum party recommendation is Level 88 for the fourth level of the challenge, but that will not unlock until Adventure Rank 28.
Depending on the difficulty level, the Taishan Mansion can drop Teachings of Gold, Guide to Gold, and Philosophies of Gold. You can also upgrade these materials into the higher tiers by using the Alchemy Bench.
Remember, you will need 20 Original Resin at the end of the challenge to be able to claim your reward, and this will limit how many times you can run Abyssal Domains each day.