A non-conductive silicon iron as used in electric motors to hold the wire coils in place and a copper that would actually conduct well to make windings. A printed motor core would need to then be dipped in enamel and baked for insulation to prevent the windings from shorting out.

Actually it would be a core for a wind generator not a motor, and magnets installed on the armature so when spun the coils produce electric form the magnetic flux as the magnets pass by.

To be able to print such a thing would be fantastic, and with a 3 extrusion head and the correct filaments it should be possible one day. A good insulation filament to eliminate the need to dip and bake in enamel would be great also.