Here's what people have said about working and interviewing at John Lewis.
What could you bring to the position.
Are you a Customer focused person.
Can you work as part of a team.
You should dress in a very formal suit
As detailed above but you also have an individual assessment where you are asked competency based questions. If you Google that phrase and have some good examples prepared it will give you a head start.
Read the details on the job application hub about what is expected of partners. The partnership behaviours are openly displayed online and you need to ensure that you meet them.
Make sure you participate in the interview - it's an instant "no" if you don't talk during a group interview!