Christmas eve and day in Nuremberg

With "Christelmakcht" I guess you mean "Christkindlesmarkt", really a different one, clossinf Dec 24:
http://www.christkindlesmarkt.de/en/

If noboy is answering I suggest to raise that question to Nuremberg Tourist Office.
https://tourismus.nuernberg.de/en/contact/

With the exception of the really big cities like Berlin, nearly everything shuts down in Germany by 2pm on Christmas eve. The 25th and 26th are both public holidays. Things re-open a bit on the 27th, but many restaurants and shops remain closed through January 6th and people take vacation during that time.

That said, some restaurants will be open. I recommend doing research now into appealing restaurants that are advertising a Christmas dinner and Christmas brunch (keep in mind brunch in Germany is also not at all like American brunch. Enjoy your buffet of cold cuts, boiled eggs, and cheese slices! Oy.) You will want to reserve for both or else you may find yourself eating Christmas Chinese or Doener Kepab dinner.

Museums will be closed. I don't know of anywhere that does parties or balls on actual Christmas eve or day. Again, do a research deep dive or you may find yourself quite bored.

There will be restaurants open 25 December for a traditional goose dinner etc. the usual time for Mittagessen 11:30-13:00. I am outside Nuremberg, so unfortunately I cannot recommend any. You can search for: 1. Weihnachtsfeiertag Gans Essen Nurnberg, but I did not have much luck. Reservations will be paramount for the best locations. Not sure the tourist office will help, but maybe your hotel can or inquire at traditional Gasthaus, Landgasthof and Restaurants you find on the net. There are parties 24 December publicly at bars and such late after family celebrations and gift opening are over, but mostly for the younger crowd getting drunk and having a good time reacquainting with friends over the holidays etc.