My father is 56 years old which is from what I understand does not need to write the test but he got a letter couple weeks ago to visit the CIC for veriication. I presume he will undergo an interview of some sorts.
Does anyone know what questions will be asked from him.
It depends on when he applied for citizenship whether he has to take the test or not. See: The citizenship test is the last step before the citizenship ceremony for nearly any person who wants to become a Canadian citizen. You need to prepare for the test and know what happens after you take it.
Who has to take the test
You must take the citizenship test if you:
are between the ages of 14 and 64 when you apply for citizenship, and
meet the basic conditions for citizenship.
Otherwise it is to check his passport to determine if he has 4 years residency. To see if he is able to communicate in English/French.