In an interview with my father about his life, what sub-headings should I use to organize the questions?Such as childhood? career?, personal life?

I would say that the subheadings that you use should be
based to some extent on what issues you really want to address (what you are especially
interested in) as well as on what has happened in your father's
life.

I would agree that childhood and career and personal
life are good ones.  But are there other things?  Did he move from place to place, for
example?  If so, you could ask about various places he lived.  Did he serve in the
military?  Did he face any significant decisions that he had to make?  Any particular
hardships?

All of these are things that you might ask
about.  When I did a similar thing with my father, these were some of the major
categories I used (except for the military) because I knew my father had had many of
these things in his life.

So, I think you should tailor
your questions to his life and to your interests.