Donald Duck can be found regularly at the Disney Parks. At Walt Disney World he can usually be found hanging out at Mexico in EPCOT and in his explorer outfit in Dinoland USA at Animal Kingdom. In the Magic Kingdom he is in always at the Silly Sideshow. At Hollywood Studios he regularly appears around the hub.
At Disneyland, Donald can be found regularly on Main Street USA. At DC he may appear at Paradise Pier near Ariel's Grotto.
In Disneyland Paris Donald can be found pretty much randomly in any land (Fantasyland, Adventureland)! Donald also can appear in Production Courtyard in the Studios.
In Tokyo Disneyland, Donald can be found mainly in World Bazaar and American Waterfront, but he also appears in many other places all the time - the Japanese love Donald Duck!
In Hong Kong Disneyland you are most likely to find Donald on Main Street or at the Fantasy Gardens character greeting area.
On the Cruise Line, Donald appears at select times throughout the sailings. Check your Personal Navigator for details.