Catalysis of the reaction: chitooligosaccharide with N-acetylglucosamine at nonreducing terminal + H2O = chitooligosaccharide with glucosamine at nonreducing terminal + acetate. This reaction is the deacetylation of a chitooligosaccharide at the nonreducing N-acetylglucosamine residue; chitooligosaccharide are composed of (1->4)-linked D-glucosamine (GlcN) and N-acetyl-D-glucosamine (GlcNAc) in varying proportions.