for my 6th form interview I was asked a wide variety of questions, I can't remember all of them but I'll try to list as many as I can as well as how i responded to them. My responses aren't perfect but if you are really stuck on what to say I don't think it will be too bad to just regurgitate what I say
"Why do you want to come to our school?"
Your school is good in -these subjects- and I want to further develop my abilities in -these subjects-
"Describe your current school"
Didn't really like my current one which was why I wanted to change schools, so I simply went with saying "It's a friendly and welcoming school, I see a few new students very year and they are always welcomed and get absorbed and become part of the community very quickly"
"What are your favorite subjects?"
Mathematics, because I like thinking and figuring things out.
"What aspirations do you have for the future?"
I want to go to Imperial College (not the case anymore but that's what I said like 2 years ago when I had this talk). I was one of the six scholarship awardees for my performance in this WCA maths competition, and went to a summer camp for Maths and Physics in Imperial College for 2 weeks and I really liked the place so I want to go there.
"What are you currently studying in your Maths classes? *proceeds to ask maths question on topic*"
just watch out for this one, the question was fairly easy though so i didnt have any trouble with it
"Do you have any questions for us?"
What do the boarders typically do at your school during weekends? (made up some random question cuz didnt have anything better to ask)