For everyone wondering, there isn't anything mysterious about NU's interview. Prepare like you would for any other interview and you will be fine. There isn't really anything to prepare for specifically. As was mentioned before, there isn't any way to prepare for the writing portion.
As far as shadowing hours, no I wasn't asked about it, but I would recommend being able to articulate what you know about PAs and why you want to be one (and shadowing obviously helps with that). A good portion of my PCE was spent working directly with PAs so that could be a factor too.
Overall, I would say don't be too nervous and just be yourself.