Assuming subjects and skills refer to book-learned knowledge rather than life experience: I'm trying to decide what to study in college or through MOOCs like those offered by EdX or Coursera or whether or not I should choose a business or a non-business major. I am trying to decide what to focus on. If I self-studied instead, I wouldn't have any debt from my degree but could still need a degree for other reasons. What specific topics are essential for entrepreneurs to know? For example, there's a lot to learn as a finance major and I'm not sure which topics would be relevant for entrepreneurship. I've tried thinking about it in other ways, for example: "What should a successful entrepreneur/CEO be able to do?" and tried to figure out which subjects will teach me the skills I'll need to achieve those goals.
Marketing & Sales. A lot of entrepreneurs are "doers of the thing" but at some point, you're forced to take the shift and become a "marketer of the thing".
Think of it this way: You can have the best product on the market, but it doesn't matter if noone knows about it.
Ofcourse, there are so many other important bits I'd love to tell you about - but, start with these and you will see traction, the rest will follow.