Domain Experts / Subject Matter Experts / Industry Experts have invaluable knowledge that you can (and should) apply during your UX process. Domain expert involvement is not an alternative to UX research, and a domain expert is certainly neither a “user expert” nor a designer.
Interviews
Domain Expert Interview — UX Knowledge Base Sketches
Creating Empathy Maps is useful for synthesizing research data in order to better understand the users. Empathy Maps are great for creating Personas, identifying users with different mindsets.