Learning about what you don't know will be clear once you think of a project you can do personally or maybe work related. So my advise would be creating a small project for yourself. If you have no clue what to build, base it on a personal problem, for example "I have difficulty waking up". Then create a design challenge for yourself e.g. "I want to create an alarm clock that wakes me up every day, so I can improve my sleep pattern". Maybe you can even pick a target group e.g. "Developers who use their computer on a daily base, and receive a lot of blue light, which affects their mental condition." Based on their wishes and needs you can create a requirements list. Based on this requirements list you know what you will need for your app e.g. "I need to save the user data in the database". Then you can search on the internet "Python databases pros and cons". Maybe I went a bit to deep into creating a project, but the conclusion is simple: create a small project which helps you find out what you don't know.