To be honest he could ask you anything if its in the regs!
Favorite is RCD max trip times on various tests, values of Ze etc.
Others are bathroom zones, switch heights.
He will also ask you to perform a few tests and compare them with the test results sheet and then ask you to interpret the results.
Remember, its one thing to be able to perform the tests but you must be able to say WHY you do the test and to interpret the results.
One last bit of advice is before you do any dead tests is to ensure safe isolation.
PROVE DEAD!!!!!! with a good voltage indicator.
If you fail to do the above then it could be an instant fail.
Good luck!