Car has error of cylinder 1 misfire and knock sensor malfunction, help?

My car is having the engine light on. I took it to Advanced Auto Parts and they hooked it up to their diagnositic machine. It came up with cylinder 1 misfire, knock sensor malfunction, and two other issues. Well the advice they gave me was to replace to spark plugs and that would more than likely fix the issue. Well, needless to say, it didn't. The engine is still running sluggish (like a misfire) and the knock sensor malfunction was still on. I am trying to see if you have any idea why this could be happening? Thanks.