I will be travelling with my minor son (17 yrs) from South Africa to Germany later this year. He is South African and German citizen. The passports have different surnames. Firstly, on which name must i book the ticket? Secondly, which passport does he have to use when during his travels?
You can use either passport to make the flight booking.
At South African immigration, show the South African passport, and at German immigration, the German passport.
If checking in luggage, show the German passport at the bag drop Counter at the South African Airport, and the South African passport at the German airport.