From what I know, czy ja was znam translates to "do I know you all" as was implies plural? am i wrong?
"Do I know you all?" means "Czy ja znam was wszystkich?". "You" means in Polish "ty" - sinuglar as well as "wy" what is a plural, so you don't need to use "all" to imply plural. Using "wy, was" in place of "ty, cię, ciebie" is enough.
Sorry if I'm not speaking clearly enough, I'm a Pole and I still have problems with English :)
'You all' or 'y'all' or 'you guys' are non-standard second person plural pronouns that exist in certain dialects of English. As such, 'you all' is an exact equivalent of „wy” and it's even accepted here(because at some point the decision was made to accept these everywhere in the course, as it makes sense and makes lives easier for speakers of these dialects). ;)