I was wondering what sort of questions may appear on the written paper
Look up past ISAs, ideally on a similar/the same area of the syllabus, and get an idea of it from there (also think back to your AS ISAs).
From what I've seen, it requires confidence in the area of the syllabus and the ability to apply it to unseen things as well as think carefully about how experiments work, sources of error, how to be careful etc, which you learn not only through theory but practice as well.