Serial Numbers? Try here: Some websites to help PP/PPK owners ID their guns - WaltherForums
Proof Mark: "Eagle over N" is a German nitro proof, according to the 1939 law. This law was in force until 1950.
Since German-designed pistols were not made in Germany after 1945 and before 1950, I think that it's almost certain that your gun was made during the Nazi era. However, you do not indicate any government acceptance marks, or wartime manufacturer code, so it may have been made for export, for civilian sale, or as a Nazi-Party gift.