Jewish people could not own guns (along with any other group the Nazis didn't like) and anyone else had to apply for a licence. It should be noted that after 1945, guns were banned in Germany for 11...
You could be referring to a number of firearms. In the US, it's typically a reference to the small calibre firearms made by the 'ring of fire' companies, such as Lorcin, Jennings, Bryco, Raven, and...
Any of the many firearms used by the Nazi Germany can be called Nazi guns. Generally this means they have waffenampts, or official inspection stamps of the Third Reich.