I sense two questions.
1. What kind of role should I play? Should I be a doctor or a lawyer, a salesman or a programmer? This is the question that the chapter addressed, and I think this question is easier. It should be obvious whether you would rather be a salesman or a programmer. It can get harder as you try to discern between two similar jobs: sales or management, mathematician or professor.
I believe personality is partly biological, and you should try to go with your natural grain. The Myers Briggs theory helped me, although at first it was hard to grasp. The best way may be to do a web search for each of the 16 personalities, read a few descriptions, and decide what you are based on that, instead of taking the tests. The theory may be pseudoscience, but it seems close to the truth.
2. Where should I work? Should I work at a website for finding restaurants or in healthcare? Should I work at Uber or Lyft? Or a nonprofit? Should I found my own start-up? If so, what should its product be? I think this question is harder for most people, and I don't have a sure theory for how best to tackle it.
What I'm coming around to believing though is that you get no meaning out of serving yourself. Sure, you need to take care of your needs, but if you try to find a job to fulfill yourself, you wind up empty. Instead I begin to sense fulfillment when I focus on helping other people. So, maybe ask questions like (A) What am I good at, or what do I have to offer (this is question #1, above). (B) What needs are out there, and (C) What are the opportunities within reach to mix A with B? Maybe start with small steps.