mortgage S&T

This is just a general answer about the kinds of things you could inquire about and I would expect someone else to chime in with more detailed mathematical answers:

I would say it would be nice to know the context of your business--how world events and other domestic current events impact mortgage rates (e.g. quantitative easing); who the major players are in mortgage purchases and insurance and what their roles are (e.g. Fannie Mae, Freddie Mac, GNMA, FHA, VA); difference between explicit and implicit guarantees; fundamental differences between CMBS and MBS cash flows and assets; expected mortgage default rates (historically in the low single digits); typical life of an American mortgage prior to refinance or sale (7-10 years); whether or not MBS and Treasuries are connected in their movement (they aren't, by the way); basic bond pricing; knowledge of regulatory bodies (FHFA; Federal Reserve; states); basic knowledge of Dodd-Frank and the fundamental changes associated with it; knowledge of who typical mortgage investors are; etc. I would even be prepared to talk about the financial collapse and the history surrounding it.

The mortgage business has a breathtaking amoung of moving parts--really learning the context of your business will take years, but it's good to know some of the basics.