The calculated distance (air line) between Duisburg and Knokke-Heist is approximately 151 miles respectively 243 kilometers.
By car or train, the actual journey to Knokke-Heist is certainly longer, as only the direct route (as the crow flies) between Duisburg and Knokke-Heist has been calculated here.
Air line (approximately)
243 kilometers
131 nautical miles