The Sims 4's Doctor Career comes via the Get to Work Expansion Pack and is one of the most challenging Careers I've ever covered. In this Career, you will start with janitorial duties, interruption of actual Doctors with socials, and patient relations and proceed to being able to run your own tests and diagnose patients. As you go forward, the Career gets more defined although menial tasks will still pop up as objectives.

How to: Doctor Career Cheats
Press Control + Shift + C then type testingcheats on and press enter. You can now get promotions with careers.promote doctor - you can also see all Career Cheats or visit a full list of Cheats in The Sims 4.

General Advice for Doctor

  • At level 1, you won't have much to do regarding patients. Try to do things that are nearby in order to raise your performance. You have two days to get promoted, so it should be easy. Don't stay late, because two days is plenty of time to get your first promotion. 
  • At level 2, when your objectives change to feature more of treating patients, look for those that have already been diagnosed. This is required for the promotion. 
  • At level 3, you should see more medical tasks - lots of 'Examine Patient' interactions. You can then Transfer Case to a Doctor after you have done enough tests. Let new objectives come in as you clear them, so that you don't waste time. You may be called to do temperature, then check eyes. Pause to be more time-efficient, as objectives take a moment to come in. 
  • Levels 4-5 can be a little tough, because you're not quite able to diagnose a lot of patients and will fail things like treadmill tests. Try to avoid those until later, while focusing on completing objectives to raise your performance. Try to get the two diagnoses down, but do not fail on them or you may end up losing huge chunks of performance - like a whole day's worth. Make sure you're right by looking at our symptoms list. It may not be as hard for you as it was for me if you can use the process of elimination along with the 'Diagnosing Patients' section below.