Professional means, we do it for a living....its what we do for our day to day jobs......in a variety of ways.
High performance, offroad, transportation, distance, exploratory, concept testing....etc.
Basically, you need to get a few high performance (in a variety of fields) driving courses under your belt (not just driving school from when you turned 16

) and start looking for work related to that through manufacturers, performance and design shops etc.
What got my "designation" is the addition of a variety of emergency driving courses (for law enforcement) high performance driving through Ford Canada, and driver of an amateur class rally vehicle....and now we run our own thing, plus provide services to one of our sponsors in performance testing.