I wish I knew more about...
1) Geography. (I have a terrible sense of spatial orientation and while I'm good at memorizing routes, so I don't usually get lost, I have no idea how our local roads link our local towns together. And forget anything on a larger scale!)
6) Game Theory. (sounds so cool, makes so little sense to me)
7) Native American culture.
8) Religions other than Christianity.
9) Making candy.
10) Making cheese.