As I recall, it was primarily science and history, with a healthy helping of the arts. (Music, painting, poetry, literature, etc.)
A lot of colleges have Quiz Bowl, but it's nothing like Knowledge Bowl. Instead... well, here's a comparison.
In Knowledge Bowl, you have three teams of four, with up to two substitutes to switch in halfway through the round. A question is read, and anyone can ring in. The first team to ring in has 15 seconds to discuss their answer, which the captain then says. The captain can delegate if they're unsure of pronunciation or something. If the team doesn't come up with anything, it's the captain's job to think of their best guess, or otherwise not answer. If they get it wrong or run out of time, the second team to ring in does the same, and then the third if they fail. 50 questions is standard for a round, with a short break at 25. The average team matchup ends with scores of around 5-15 for each of the three teams. My team, which was probably the best in the state bar none last year (we beat the 4A and 3A state champion teams on three occasions), could rack up as many as 30, but anything more than 20 is really rather good.
In Quiz Bowl, you have two teams of four. There are toss-up questions, and anyone can ring in. There is no discussion amongst teammates, and whoever answered has to answer. The tossups range in difficulty from completely insane - You have 10 seconds to come up with the volume of a particular cylinder with a particular pentagonal prism cut out of it - to ludicrously easy. (You have 10 seconds to come up with the atomic symbol for potassium.) After the toss-up, the team that won it is posed an incredibly easy question, and only they can ring in. Then they do a slightly harder one. Then a question that might make you think. Then a 'challenge question', in which the team can actually speak to one another. If they miss any of these, which almost never happens before the last question, the other team continues the chain from where they left off. There is a certain time limit for a round, usually 20 minutes. Point values are 1 for a tossup, 3 for the first chain question, 3 for the next, 5 for the third, and 7 for the challenge question. Just about every question is answered correctly by one team or the other because of how ridiculously easy most of them are.
The primary difference, to me, is that Knowledge Bowl is a team sport and Quiz Bowl isn't. The former grants one question per right answer, and the questions are all somewhat hard. The latter is basically up to who can ring in first on the easy toss-ups, so that they can get more and more points for answering up the ludicrously easy chain. Even if the other team gets the 'challenge question' at the end, they won't make up for you getting 12 easy points. When one team gets lucky with their buzzers, they win. Between good Knowledge Bowl teams, there can be a neck-and-neck race. One team gains a clear advantage from the beginning in Quiz Bowl and never looks back.
Weird thing for the Happy Thread, but I guess the nostalgia is making me happy.