I had a scenario like this yesterday in my interview......

"Your captain is not following the checklist properly and skipping over items, what would you do"

My response was that I would remind the captain of what items we seemed to be missing and offer to handle the checklist myself to ensure nothing is missed. I said that we have a checklist for a reason and it is important not to miss any items, as small as they may be, which might have an impact on safety later in the flight. If the captain continued to break policy and I could not solve the problem, I would mention what was happening to our CP because I would be concerned that the captains actions could be affecting the safety of our operations.

Then he said - "Ok so you reported him and the CP said there was no cause for any disciplinary action and you were scheduled to fly with that captain the next day...how would you handle it?"

I stated that I would go about my duties as normal and try to resolve any conflict the captain may have with me.

I don't think they want to hear that you would immediately run to the CP and rat out your fellow crew members. But also that you would not allow regs to be broken and do nothing about it....

(I don't think it sounded quite that good when I was saying it out loud but I think they got the point.)