Was it my plan or my technique that was flawed? Which sides of the board should I have been playing on? Tactical shots missed? Was I playing a main line and if so did I go out of book at some point(good or bad?)
What are some good post-mortem questions to ask a strong player after a defeat?

Sometimes the stronger player can give you bad advice too or they actually miss what was the critical point. A good sign is if they tell you where they made a mistake too (depending on how bad you messed up or the level you are playing).
Just ask if you can go over the game with them and let them talk. Find out what was going through their head especially if they made a move that seemed subtle. Sometimes key positional richness will lie in some random looking move. And then remember their points and go over at home yourself. This is very important. Don't plug the game into the computer until you have analyzed it yourself. If not, you are cheating yourself out of hard work and their will be a gap in your learning process b/c the computer is doing the hard work for you.
If you are lucky to have been crushed by a stronger player who happens to be a nice guy who doesn't mind going over the game with you, what are the most productive questions you could ask him in order to learn from that loss?
Most of us take the game home to Uncle Fritz/Rybka for analysis but I've always got more value from a loss if my opponent went over the game with me and pointed out key things that were evidently wrong at my end.
So to repeat => What are some good questions to ask him/her ... beyond the obvious "where did I go wrong" ?
Hope a few titled players chime in to this one ...
S.