History / ww2 polish military abreviations [4]

Hi am trying to decipher my Grandads military history, like a lot of the men of his generation he never said a word about it.

I have his military info from the Mod, other than trying to work out the hand written text; the sticking point at the moment are the abbreviations.

He is shown to be in something that is either 28.P.S.K or J.S.K in Lodz in 1934-36. does anyone know of a list of unit abbreviations?