Catalysis of the reaction: N-acetyl-beta-D-glucosaminyl-1,3-N-acetyl-D-galactosaminyl-R + UDP-N-acetyl-D-glucosamine = N-acetyl-beta-D-glucosaminyl-1,6-(N-acetyl-beta-D-glucosaminyl-1,3)-N-acetyl-D-galactosaminyl-R + UDP.
O-glycosyl-oligosaccharide-glycoprotein N-acetylglucosaminyltransferase IV activity