Finding parking in Sankt Wolfgang (especially free parking) is a bit tricky but not difficult. To be on the safe side, just take the car to one of the parking lots or the parking garage near the tunnel entrance. It's worth the money to not have to worry if you have parked your car illegally.
The only road to Sankt Wolfgang approaches from the east from the small village of Strobl. You will see signs on route 158 for Sankt Wolfgang and Schafberg. Head for them and you will pass through Strobl.
The downside about having only one way to get there is that it takes quite long to get there. But the plus side is you get to enjoy the beautiful mountains and landscapes surrounding the Wolfgangsee.