I don't know because the government at this time is revising its application process, but what I can say is with respect to the predecessor process.
We have a criteria of eligibility based upon certain types of experience and background, either in the military or in adjudication. An individual applies to become a member of the board. The application is assessed against those criteria. If they meet the criteria, they're then given an opportunity to write an exam, which assesses, among other things, the ability to interpret a statute and the ability to write in a concise manner. If they pass that exam, they then go through an interview process, which consists of the chair or deputy chair, a retired Supreme Court justice, usually an HR consultant, and sometimes another board member as well, who then interview those people. If they pass that process, then they go into the pool of candidates eligible for appointment.