The best I can do is to let you know what I ask and want to talk about in these situations. I have worked with 30 Ph.D. advisees in my engineering faculty career to date.
I will not ask technical questions in the same way I would on an oral examination. But, I will certainly bring up technical ideas closely related to my research that I would expect an interested student to know at least a bit about. If the student has something interesting to say on these ideas, then I know that they are seriously interested in my research. I will say that it is better if the student admits that they do not know much about an area rather than "pretend" to be better informed than she/he really is. I'll have to say that I value honesty in these settings above all else.
I will be very interested to understand why the student wants to get a Ph.D., so she/he should be ready to talk about career goals with some specificity. In my view, it is not enough to simply say that they wish to have a career as a faculty member. Why? Where? What do they hope to accomplish?
I'd like to know a bit about their research goals. What types of research are most interesting? What impact do they hope to have with their research and scholarship? What journals do they hope to publish in?
Finally, and probably most importantly, I like to see some evidence of passion about a research problem or subfield or a particular aspect of academic research or the academic career. Students who have a passion to accomplish something and then can set goals that enable them to make it happen are the ones we want to work with most.
I hope this helps!