One solution is to read books that have survived the test of time (e.g., Descartes).
Even scientific books that are out of date have deep insights into nature for example the origin of species, what is life?, and origin and history of conscientious.
The exceptions abound, of course, but categorically speaking, you only need some technical knowledge. It's the "how to lead your life" knowledge that is harder to glean, and one most resistant to taking a head-on approach like studying all the philosophers and then ranking their greatness in a spreadsheet.