I can't seem to get the meaning of this sentence: "N' pa konn sak blan sak nwa" Is it 'we don't know a white sack from a black sack'?

No.  I'm not reading it that way.  I think it's missing a couple of apostrophes.  Maybe if I rewrite it (the way it should have been written) you might get it:  There it is: Nou pa konn sa'k blan sa'k nwa.