[RolandF]

As you all know - Germans love to create word behemoths like Donaudampfschiffahrtskapitänswitwe or similar. To make it more readable, oftenly hyphens are used like Donaudampfschiffahrts-Kapitänswitwe or Donau-Dampfschiffahrts-Kapitänswitwe. Both versions are correct.
Jaaps abbreviations are correct, too. With the exeption of #3, #4 and #6.
They derive from two word variations:
Werknummer and
Werk-Nummer
Both are correct because of the above-mentioned reasons.
So it depends on how much time and space you have to spend if you write huge lists or use it only for a single time.
Personally I´d prefer Werk-Nr. or W.Nr. In German the dot always significates the use of an abbreviation.

But don´t use Werkenummer or similar ;-)

Regards
RolandF