Flight ops interviews tend to go around any flight ops experience, and about how flexible are you working various shifts and nights in addition to the usual general interview questions.
Having CPL an IR will help with understanding the flight planning software, but having working experience with flight planning system is an advantage. It all depends on the skill level the company is looking to employ. If its a entry level ops position, then i'd expect general interview questions. If they are looking for someone with ops experience, there could be some technical questions on flight planning. A major airline can also give you a multiple choice test on flight planning, or you could be asked to decode a flight plan.
I hope this helps.
Best of luck at the interview.