One probably anticipates the most likely questions. One gets information, if one can, about the personalities of the examiners [and] the kinds of questions they're likely to ask. One becomes familiar with one's own work. It's almost always true that the answer to a question that an examiner asks will be there in the thesis. The most effective response is to say, "Well, I tried to address that issue in this chapter or in these pages," and then to go on and perhaps expand on what you were able to say on that topic in the written text of the thesis. Or, indeed, if the examiner hasn't paid sufficiently close attention to what you've said, then to reiterate what you've said, to stick to your guns and say, "I really believe this; I think I've presented the evidence to answer that question in the text of the thesis," and politely, in a dignified way, remind the examiner that in fact the answer to the question is in thesis and expand on it if you can.