Quoting: z_darius
Copernicus was born in Royal Prussia, i.e. under Polish jurisdiction. Polish citizneship is based on ius sanguinis and ius soli. Therefore he would get a Polish passport.
Polish citizenship is not in the slightest bit based on jus soli. A child born in Poland to parents who are not Polish has no right to a Polish passport unless it would otherwise be stateless. So even if we agree that Royal Prussia was actually part of Poland (which is a bit of a stretch, would you like to claim that another well-known Prussian, Field Marshall Hinderburg, is also a Pole?), merely being born on Polish soil would not have given Copernicus Polish citizenship.
Would he qualify under jus sanguinis? Probably not. As you have said before, we know little about his father's early years. However we do know that he accepted public office in another country (Royal Prussia) and before 1951 that automatically resulted in loss of Polish nationality. As his father took office before Nic Junior was born, he did not have a Polish father because his father's Polish citizenship had been taken away. What about his mother's line? Well her parents were not Polish: Lucas Watzenrode the Elder was the child of a German trader and his wife was named Katharina von Rüdiger, not the most Polish of names, if they were not the children of Polish citizens (they were not) and they had not naturalised as Polish citizens (they had not), Barbara was not Polish.
Of course, we could agree that Royal Prussia was in fact Poland and because Copernicus lived there he could have applied for a Polish passport as a naturalised citizen. Well, he could if there was any evidence that he spoke Polish. There isn't, and knowledge of Polish is a requirement for naturalising. Oops.
Of course, with a German mother he would have got a German passport without any problem....