Based on my experience, the 2nd interview is a formal panel interview consisting of the school head, your immediate boss who interviewed you at the first interview, a 3rd party (from another school within the poly, to give a neutral viewpoint) and a HR rep.

As usual, they will not ask any technical questions, and expect to repeat what you may have said in the first interview, especially on your relevant experiences, goals and expectations, etc. They will also ask you about the challenges in your field of expertise. The one that I went through, my immediate boss did not ask anything, and sat there like an observer.

This session is more of letting you impress your big boss.