A salsa recipe uses green pepper, onion, and tomato in the extended ratio 2:5:9. How many cups of onion are needed to make 96 cups of salsa?

The ratio of onions to the total ingredients is 5/(2+5+9) = 5/16.

Thus, 96 cups of salsa need 96 * 5/16 = <<96*5/16=30>>30 cups of onions. Answer: \boxed{30}.