How much do I need to know about government prior to attending community college?

You don't really need to have prior knowledge about government. I have taken college courses that I hadn't taken in years since high school and have been successful. If these subjects are more difficult for you then you probably need to spend more time studying, but they will teach everything you need to know. It also helps to get a good professor. There website ratemyprofessor.com should have listing of teachers at your community college and how they were rated by students. This is how I always pick my teachers.