Not sure if that's particularly helpful, but my DD found KGS exams to be very straightforward. Both maths and English. She said there were no tricky problems in the maths exam and she wasn't pressed for time. In English, it was also pretty straightforward with 2 options for the essay - one related to the text. That's what she chose.
She did have a bit of a wobble on VR - it is a typical GL format and we were practicing based on methods from Patricia (from this site), IPS Technique book etc and were used to writing on exam paper, doing loops, etc. That was not allowed in KGS exam so she had to re-adjust on the spot and in the end ran out of time and had to guess the last 2-3 questions.
That said, she was still invited to sit the scholarship exam and got the scholarship. The scholarship exam was more difficult and KGS is unusual in having a separate exam among London day schools. This must explain why the main exam is straightforward as they can then throw more difficult stuff into a separate paper.
Can't help with the interview as DD had a scholarship interview rather than standard, but I would imagine it's pretty similar. Apparently, they do a general chat and then focus on a weakness. In DD's case, she didn't solve one of the maths problems, but we solved it back at home and that's exactly what they asked her in her maths interview. In English, it was types of literature she likes, why, favourite character and I think she also had to analyze a poem (but I might be confusing with another school). So basically if your DD comes out of the exam and can remember what she didn't solve/not sure - go over it with her. Likely they will focus on this at the interview.