You can start with what you already know and then build over it, or diversify, with time. The easiest way to monetize your knowledge to create a blog and link i

You can start with what you already know and then build over it, or diversify, with time. The easiest way to monetize your knowledge to create a blog and link it up with social media (twitter, FB, youtube etc). For example, you can write about management and backend data processing (what you do at work). This way, you don't have to learn something new to start your side project (except maybe how to manage a blog). The blog can be monetized via Ad networks like Adsense and Amazon affiliate program etc. As you grow, you may take in direct advertisers, sponsored content etc.