When it comes to learning about business, Elon Musk does not turn to popular management gurus or bestselling leadership books. The SpaceX and Tesla chief has long relied on reading as a source of knowledge, drawing lessons from history, science, engineering and the lives of great innovators rather than conventional business literature.Following that philosophy has helped Musk build one of the world's most valuable business empires. The entrepreneur recently became the world's first trillionaire after a blockbuster stock market debut by SpaceX sent the company's valuation soaring. Investors backed the space exploration giant despite its heavy spending, betting that its…