re: How did the Germans know who was Jewish?

"Everyone knew the genocide was coming". Totally not true re the general populations. There are 1000's of stories from Holocaust survivors stating that for many, the older members of families refused to believe that extreme, trapping families till it was too late. Still again, 1000's of Jewish veterans of WW1 refused to believe that they would ever be persecuted, let alone murdered. And once it became common for Gentile citizens to be allowed to take over Jewish homes / property whose owners were forcefully evacuated, the general population in Germany & in countries that were invaded & conquered turned in Jews by the 1,000's.