Collins German Dictionary: working knowledge - Grundkenntnisse
working 2 adequate for one's purposes • a working knowledge of French.
http://www.chambersharrap.co.uk/chambers/chre..."A working knowledge gives you the basics of a topic, enough light so that you won't hurt yourself as you move on to more complicated territory. It isn't complete knowledge, but it's enough to tell you what the topic entails ..." (from the book "Research Strategies" by William B Badke
http://books.google.com/books?vid=ISBN0595313..."working+knowledge&hl=de&sig=uSgej9hW_XA1MhNdwjRSpVLkUg0)
"Praktische Kenntnisse" sounds to me as if you do not know much about theory, but "working knowledge" does not imply that:
"Working knowledge of the theory, principles and techniques of staff development"
http://www.cs.state.ny.us/tsplan/tsp_getpage...."A good working knowledge of the theory of conflict analysis"
http://www.ciian.org/courses1.shtmlAlso, "praktische Kenntnisse" does not get across the fact that you do not need advanced knowledge, but only need the basics, which "working knowledge" definitely implies.