If I'm serving a corporate audience, do I market to the boss who writes the checks or the person who would sign up to the list or enroll in a future course?

You should talk to the person that would consume your content and actually get value from it. If they have to talk to their boss to get approval, help them with the language they should use. You could even provide them with a script (and use that as a lead magnet to get them on your list!).