as a self taught software engineer just starting my career; what do you mean by domain? I'm familiar with the term as i have spent years on learning web development as the "domain name" like in a url. But i get the sense that you may be speaking on something else? I will agree though; my boss should learn more about the web and how it works instead of relying on these frameworks to handle everything...
Basically what @clobble_wobble said. For a fast introduction I recommend Domain-Driven Design Quickly (available for free). If you are interested in gathering requirements in a way that can also strengthen your understanding of the business domain, you may want to check the Event Storming technique.