First of all, I think you should definitely take a direct interest in the contact that your professor is teaching you. I would ask critical questions (How's? Why's?). This will let you professor know that not on are you actively listening to the content, but you genuinely care about the content and seek to better understand it as well.
If you are also interested in the subject matter, don't be afraid to ask more personal questions to your professor as to what made the interested in their specific career field/content. Why are they passionate about their fields? What were the steps they took to becoming a professor? Who or what inspired them? In my experience, professors are always open and even excited to share their journey's with their students, so don't be afraid to ask!