First you take an online Personality assessment, then if accepted, you get interviewed in person at the Hinckley site. If you do well, then you reach the last interview with a senior engineer. However, I didn't get to do the second interview.
Know the basics of thermodynamics, materials, manufacturing and components involved in a motorcycle.
Don't stress too much, the engineers are welcoming and really makes you feel at ease. Do your best and good luck!