Junior's is a good bet. However, in Brooklyn there are many Orthodox Jewish neighborhoods. They are not likely to have classic delis, but if he is after Jewish food, places like Crown Heights, Borough Park, King's Highway, Williamsburg, or Midwood might be worth a visit.
In Williamsburg you might try Gottlieb's (352 Roebling Street). In Midwood, you might try Essex on Coney (1359 Coney Island Avenue), but I would choose Katz's or Second Avenue Deil in Manhattan.