Lots of online testing, including a numerical one. The a partner interview that was competency based, where they asked you to give examples of when you have shown a certain capability.
For men, a suit and tie would be recommended.
1: HR manager - motivational
2: Audit Manager - technical
3: Audit Partner - Personal
The obvious such as researching KPMG and the particular role you are applying for. There appears to be a greater focus on diversity and inclusion so it's worth having a read up on that.