Hydrolyzes the N-glycolyl group from N-glycolylglucosamine 6-phosphate (GlcNGc-6-P) in the N-glycolylneuraminic acid (Neu5Gc) degradation pathway. 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.