Hydrolyzes the N-glycolyl group from N-glycolylglucosamine 6-phosphate (GlcNGc-6-P) in the N-glycolylneuraminic acid (Neu5Gc) degradation pathway. Although human is not able to catalyze formation of Neu5Gc due to the inactive CMAHP enzyme, Neu5Gc is present in food and must be degraded. H2O + N-acetyl-D-glucosamine 6-phosphate = acetate + D-glucosamine 6-phosphate Binds 1 divalent metal cation per subunit. Amino-sugar metabolism; N-acetylneuraminate degradation. Belongs to the metallo-dependent hydrolases superfamily. NagA family.