The point of the report is to start the day's discussion; the topic is anything relevant to the day's reading material.
Feel free to read a short (one-page-ish) prepared report, to speak from notes, or to extemporize, -- whatever makes you comfortable.
A good report will raise as many fruitful questions as possible and get discussion rolling. Try to raise questions and suggest possible answers, but you needn't work out elaborate theses. I'll do the first to provide a model. These are not research projects; you needn't do any outside reading to prepare for them. But if you feel some outside reading will improve your ability to start conversation, feel free. Anything else that will help -- handouts, short readings for the rest of the class -- is welcome and encouraged.
You can focus on any aspects of the readings you like, although, again, the broader the coverage, the more likely it is to start discussion. If you want to draw the class's attention to a particular passage, you may want to E-mail them in advance -- for instance, "I'll focus especially on chapter 4 of part 3, so you may want to re-read that part." When two people are reporting on the same day, they can contact one another in advance and work out a plan for working together, but it might be more fruitful not to pre-arrange anything.