Transfers sialic acid from the donor of substrate CMP-sialic acid to galactose containing acceptor substrates. Has alpha-2,6- sialyltransferase activity toward oligosaccharides that have the Gal- beta-1,4-GlcNAc sequence at the non-reducing end of their carbohydrate groups, but it has weak or no activities toward glycoproteins and glycolipids. . This is the function of ENSG00000144057 (ST6GAL2, ST6 beta-galactoside alpha-2,6-sialyltransferase 2).