Keep in mind that you can only make an Engineer specialist if you have a building that allows for one, like a Forge, Factory or Industrial Park. If you don't have any buildings that allow you to have a specialist, then you won't be able to. Other than just the regular Citizen specialist. If you want Scientists you need Libraries or Observatories, Merchants need Markets or Grocers, an Artist requires a Theatre or Broadcast Tower. Priests need Temples.
Scientists, merchants and artists can be also be run by using the Caste System civic regardless of what buildings a city has.