Hi there,
1) Should I focus on their industries or I could get any industry during the case?
You may get any industry. It is definitely possible that you get cases related to the background of the interviewer, but there is no guarantee. It is still a good idea to review their industries as (i) you may get a case on that (ii) you could have a discussion/question on their experience in the Q&A at the end.
2) This is for the Riyadh office, has anyone interviewed for the Middle East and therefore would you have any tips?
Please feel free to PM me if you have questions on the process, I helped several candidates to land offers at McKinsey in ME offices and know 30+ real questions asked there.
Best,
Francesco