Actually, in the 08 version of the rulebook, on page 27 it states:0 vs. 0 is self explanatory, KO has to beat your armor protection number so a 0 KO (0 poison, 0 disease) will NEVER EVER do anything.
Basic Knockout
With this skill, the Rogue is able to render a target unconscious. To perform a knockout the Rogue must strike a target in any legal target area with a tiny weapon or a fist phys-rep and call the # and knockout. Thus, at this level the call is “3 Knockout.” If the characters involved are not in an active combat situation, Rogues may lightly touch their target with the pommel of a weapon to perform the knockout. If the target has three points of armor or less at the time of the knockout, the target falls unconscious for five minutes. See Knockout on page 82 for more information. This skill takes an uninterrupted 10 count to charge.
I always thought the number had to exceed your armor 'value' to take effect, but apparently not.