I fly a business jet with no cockpit door but unruly passengers aren't an issue.
So, the assumption is that you're considering the "UK" situation. Therefore, cockpit/flightdeck door is locked. If that's the case, you'll have FAs and so they'll deal with said pax. The SOPs are that you do not leave the cockpit.
However, what if you're being interviewed for an airline that doesn't have FAs and doesn't have a door? Now you'll have to think about that situation.
Generally, the SOPs will have some guidance.
With interviews, they are looking for someone who knows when to follow the SOPs and when to step outside them - simply because there is not an SOP for every situation.
They are also looking for someone who knows how to ask questions without annoying the captain but also someone who can be assertive when required. It is a fine judgement act and occasionally, you'll get it wrong (as I did).
So, for me to give you the "correct" answer is impossible. You are expected to have thought about it and to come up with your own. There is no right or wrong, just better. If you're a low houred pilot not working as a pilot, then of course, you won't have the "perfect" answer - but the interviewers are expecting you to have an "idea" about how it will work.
If your profile is correct, you're 43 and thus can draw on "life experience". Use that, chances are it's correct.
Good luck.