will they get zapped after im done zapping the knob i what im trying to say.
No, the door knob cannot retain an electric charge. If you held the bug zapper to the door, then they could potentially get shocked (since the door knob is a conductor, but not a capacitor).
Clayby said, No, the door knob cannot retain an electric charge. Not true. A metal door knob can store an electric charge if it is electrically insulated from everything else. I don't fully comprehend the math, but I believe that the amount of charge it will hold is proportional to the voltage of the bug zapper, and inversely proportional to (something like) the surface area of the knob. This is not accounting for the fact that a high enough voltage on the knob could cause some of the charge to leak away because of corona discharge. In practical terms though, the amount of charge that will be stored on the doorknob most likely will be somewhere in the realm of not-enough-for-the-victim-to-notice.