CASA do not appear to have any standard CP interview process. At entry level GA they may make a big deal out of a flight planning and loading exam - I dunno because I never had to do a formal exam with them. Maybe they assumed I knew that stuff already, HA HA. Seems a bit pointless if you have recently done all your ATPL theory.
They will want you to know something of the Civil Aviation Act, particularly Section 28 where it bangs on about duty of care, provision of facilities etc. A good working knowledge of CAO 48, or if your employer runs the 'standard' exemption, that too. IFR recency, maybe a practical exercise with a MEL etc. CAO 82.3 from start to end.
A lot depends on what sort of reputation your employer has with them. If they are a bit dodgy on maintenance, expect a grilling in that area, if dodgy on performance, in that area etc.
The 'wotif' could be anything from how to deal with the boss's favorite son/daughter who wants to fly but is useless, to an irate customer demanding that you press on into bad weather, to financial implications if you were to jack up on an issue and lose your job. The answer to all of the above will vary according to how they set the scenario, but the common thread is that the CP holds the AOC and the boss may occasionally need to be reminded of this fact.
Also, remember that as CASA's delegate, they need you there as much as you want to be there. Their main concern will be that you are strong enough to stand up to the demands and pressures of the job. It will only be a poison chalice if your employer is on the dark side.
If you build a good reputation with CASA and treat your troops fairly, you will never be unemployed. Good luck