Q: Does a 9 chord have a dominant 7 or major 7
A: 'C9' is short for C dominant 9, which at minimum should include the notes E, Bb, and D, with C in the bass. If you want it to have B instead of Bb, you'd probably write Cmaj9, and if you wanted neither B nor Bb you'd probably write Cadd9 or Cadd2