What can you learn from alchemy today?

Nothing. Alchemy was abandoned because it didn't work. Some of the things that did work became chemistry. No one successfully turned lead into gold. Nor did anyone successfully create the philosopher's stone. Alchemy was basically chemistry with a lot of magic thrown into it. The alchemists were sorcerer want to be's. They attempted to conjure spirits, and use spells on chemicals that they believed contained magical properties, all in a vain attempt to convert base metals into something of greater value. Even Isaac Newton, probably the greatest scientific mind of the last 500 years, accomplished nothing in alchemy, even though he experimented with it for decades.