The list of questions on the new form is far more extensive than before. In the 'good old days' some examiners would ask one from each section, or about five total.
Now, strictly speaking, all have to to be asked, though how the examiner deals with that is probably somewhat an individual thing. Go to the check armed with your own AIP, ERSA and of course, charts. If the examiner is a
pr!ck and wants you on the back foot you will know soon enough, because he will have his own AIP or extensive notes in hand and will start grilling you. Typically, examiners with that style need these 'props' themselves, so I think it is only fair that if he needs to refer to notes, so can you. Therefore, when you don't know the answer, or are a little uncertain, admit it and look it up on the spot.
A more relaxed examiner will simply work from the CASA form, ask questions in his own words and accept reasonably close answers in your own words. He will avoid 'open' questions and won't belabour trivia. Again, if you really don't know an answer, at least know where to quickly access the information. Which, after all, is what you should do if you are planning a flight and something odd presents itself in a NOTAM or forecast.
Of course the 'biggies' relating to basic tolerances, terrain and traffic avoidance need to be absolutely known without reference. Other than that, much of the IREX required knowledge is non life threatening if you don't maintain it to theory examination standards and are out there in the real world of IFR.
If the examiner is a decent sort he will be trying to put you at ease, not hell-bent on winding you up into a lather before the actual flight.