what kind of questions would I be asked in an interview for a humanities subject at Oxford/Cambridge?

Obviously it depends on the subject that you are applying for but usually they would start off with a challenging yet well-known problem in the field. From there they will probe you in order to see where you stand on the problem. Once you give some sort of response they would question why it is that you think that that is the case, as they most probably know common responses to the view you have provided. This then continues as a general exploration of your thoughts on that topic.For example, with my philosophy interview they began by asking me whether a person could survive severe memory loss? They then picked holes in any argument I provided, Making me defend my point or reconsider it entirely.Another common interest that they have, although this usually comes out in general interviews rather than subject specific ones, is what you have been reading in and around the subject. This is done in order to see where it is that your interests lie and to see how much effort you have put into learning more about your subject.