In 2007, he granted Rolling Stone an interview.

From the interview:

1964 ... a friend gave Owsley 400 micrograms of pure LSD manufactured by Sandoz Laboratories in Switzerland, where Dr. Albert Hofmann had first synthesized the drug in 1938. At the time, Owsley was living with a Berkeley undergraduate chemistry major named Melissa Cargill. They decided to try to make acid that was "at least as good or better than any pharmaceutical firm." It took Owsley just three weeks in the UC Berkeley library to learn everything he needed to know about the process.

It can be inferred from that he learned either from academic papers or faculty and staff at Berkley. Multiple articles on the synthesis of LSD had been published at that point, the most complete and useful would be this one.

Another relevant quote:

... he did provide 300,000 hits of acid called "White Lightning" for the event. Five months later at Monterey Pop, Owsley passed out his "Monterey Purple" backstage to Jimi Hendrix, Pete Townshend and the Stones' Brian Jones, not to mention much of the festival's staff and crew. Owsley also sent a photographer back to England with a telephoto lens packed with tabs of purple acid on the condition that he share them with the Beatles.

Monterey Purple was the name of the batch that he created for that festival and handed out before Monterey Pop that inspired artists and musicians of that generation.