P2 is for Officer/NCO so will usually be given by an officer.
If you can, dress smartly, but be comfortable; you'll be spending time just sitting. Pen and paper may be provided but worth having your own for note-taking. Take something to carry home your notes and any literature you are given; rucksack, messenger bag, one of those zip-around folders.
This part of the process isn't assessed. I wouldn't expect jeans and t-shirt, but people aren't judged if they've made an effort to get there and come straight from work in a barista uniform. Same as it doesn't matter if can't answer questions. The presentation is to tell you what to expect later. Make the most of it.