I'm afraid I can't offer you much info for a Netjet US FA position. I know the FAs were group interviewed with the pilots in London (for Netjets Europe).
The format (then) was a group chat with the boss and then individual interviews that went for about 10 min or so.
I dare say you'll have to display polished but discrete grooming, good conversational skills, open personality, flexible with dealing with different nationalities. Obviously, presenting VVIP catering is a must. As you probably gather, you're teamed with one crew /aeroplane for your tour. In Europe, the tours are usually 6 on, 4-5 off. With the "large cabin" aircraft you can possibly be given longer tours with different days off. Plan 18 days a month working.
Have you looked at the Netjets website for more info regarding the fleets etc?
You could try posting in the GA and Bizjet section of PPRuNe.
Good luck.