With any questions to anyone affiliated with the a potential school you really want to focus on asking honest questions you generally would like to know the answer to. Use this potential resource primarily as a way to gain information that will inform your application and personalize essays and interview responses. Now when it comes to specific questions to ask a professor at a university here are a few categories/questions:
School Teaching Style
-Case vs Lecture
-Reported Grades
In-Class Learning
-Group vs Individual Assignments
-In Class Student Engagement/How active are discussions
Experiential Learning
Mentorship
-Is it common for students to connect with you outside of the classroom on topics
-Internships/workstudy with students
Recruiting
-How does your class prepare students for recruiting
Experience Teaching at the School
-Support of school with research
-Connection with students
-relationship with students after graduation
These are just a few examples of potential questions you could ask but again I would personalize insights you are generally looking to uncover through your conversation with them