Start by realizing that knowledge is totally useless unless you actually DO something with it.
When you invest money, the investment agency uses that money, or in other words, the money moves. You get a return on investment because the money moved, it wasn't stationary. Things were done using that money.
Knowledge is similar. If you have knowledge but don't do anything with it, it earns nothing. There are theories of economics (not necessarily agreed by all) that value is gained only through labor, through the utility of what you do. Converting your knowledge into money is simply finding a situation where someone will pay you for what you can do for that someone because of your knowledge.
My uncle Maurice told me many years ago that I needed to decide what I liked to do, then learn how to do that well and find someone who would pay for that enthusiasm and knowledge. Decide what you REALLY like and then explore how to profit from that. Easy to say... though I know it is also hard to actually do.
There is an Americanism that relates to this concept. "If you're so smart, why ain't you rich?"