I don't know much about Wengers and I was (and still am) hoping that someone knowing more than me would answer here so that I can learn from it. Since it didn't happen so far, I'm saying the little that I can.
It looks to me like a stainless steel SAK, so I believe that it's likely to be from the 1930's or early 1940's (1920-1950 should be a "safe" range). Note that the tang stamp used on this knife appears in
Ulli's table, with the range of years 1920-1945.
Value? If it was in good condition without serious issues, I would have said about $100, but it seems to have at least one significant issue: the bail is detached on one side and a part that is important for holding the knife together is missing. If this is the only real issue and the springs are at least OK (providing reasonable snap), I would say $50.
I will be more than happy if anyone with more knowledge will add it here and/or correct me if I'm wrong.