They show a live readout of the wind tunnel's current speed, in the lower-left corner of the screen showing the timer. It varies substantially, in order to adjust for different customers' weights (maximum is 300lb, minimum is in practice about 30lb though that's more about whether a kid is old enough to understand the concept of staying still) and for whether you're in the process of doing a tandem flight up to about 14 feet (regular flight is around 3 or 4 feet) or--for advanced flyers--certain stunts involving presenting less surface area to the wind (like "sitting"). It was mostly around the 150 - 210 km/h range.

Search engine suggests that freefall is around 190 km/h, give or take.