i believe it is something like this
http://www.khsbicycles.com/Images/serial_numbers.gif
for our generation of frame the serial is found stamped under the bottom bracket. thats where i found mine.. it was under the plastic cable guide that sits there, just relieved the tension on the cables, took off the 1 screw that held the guide in place and read the serial.
btw guys i picked up another old khs.. a 91 descent.. i'll put up some more details and pictures when im more happy with its condition.. lol