What you need to know as a cook..
Do you like what you cook? Do others like what you cook?
If you want to make something new.. can you make it taste good?
If you can answer yes to all three, you have the all the knowledge you need to cook. Granted, you aren't at the "chef" level. without formal training you won't get there.
Having the basic knowledge of the flavors you want and how to arrive at them is all you need. You don't need to know the names of what you are doing. I don't have know why salt does what it does, all I have to know is...this dish needs salt. If you think you have to have all that "formal" knowledge and you aren't going to become a chef.. spend more time cooking and less time reading.