Here is the local media coverage story about the tryouts held by the Gary SouthShore RailCats of the American Association. This was held two years ago, but you get a could idea of what you will experience at a typical professional independent baseball open tryout.
Become aware of upcoming tryouts by joining the notification service here: Independent Minor League Pro Baseball Tryouts
If you need some help increasing your 60 yard dash speed times, arm velocity, vertical leap ability, hitting power or improve your muscle mass for any professional baseball tryout (or private workout) then here are some resources to help you: Resources for improving your chances at any pro baseball tryouts