When my wife and I took a cruise a few years ago, we became friends with one of the cruise ship entertainers. I asked him how he got the job, and he said his agent arranged for an audition with a cruise ship activities director. The cruise line was looking for entertainers who did middle-of-the-road material, like magicians or ventriloquists or lounge singers. Stand-up comedians with PG-13 material were also in demand as opening acts.
He said working on a cruise ship wasn't as glamorous as it sounded, because he had to share a very cramped cabin with another performer. They usually had to perform other duties during the day, like host parties and direct group games. He said the best part of the job was enjoying a lot of the same amenities as guests, like the buffet meals and sightseeing tours.