The calculated distance (air line) between Bonn and Watermael-Boitsfort is approximately 117 miles respectively 189 kilometers.
By car or train, the actual journey to Watermael-Boitsfort is certainly longer, as only the direct route (as the crow flies) between Bonn and Watermael-Boitsfort has been calculated here.
Air line (approximately)
189 kilometers
102 nautical miles