Lecture #12 looked at the optimality of the A* algorithm, and the learning of heuristics.
Notes are available in two formats:
The lecture covered material from Chapter 9 of the textbook, from page 145 to 155, and from Chapter 10, pages 172-175.
You should go through this material in conjunction with the notes, again concentrating on trying to understand why A* ensures optimality (rather than being able to recreate the proof).