GO:0004577:   N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity
Catalysis of the reaction: UDP-N-acetyl-D-glucosamine + N-acetyl-D-glucosaminyl-diphosphodolichol = UDP + N,N""-diacetylchitobiosyldiphosphodolichol.