At the Magic Kingdom Goofy can always be met at the Silly Sideshow. At Animal Kingdom he appears in Dinoland USA. In EPCOT he is always inside the Character Spot. At Hollywood Studios he can be often met on Commissary Lane.
At Disneyland your best chances are up in Toontown, or in Town Square. Over at California Adventure you can meet him usually meet him on Buena Vista Street.
At Disneyland Paris Goofy is often near the Castle, in Fantasyland or Frontierland.
At Tokyo Disneyland, Goofy is often out in Toontown, and in just about every land of DisneySea at some point!
In Hong Kong Goofy can often be found in Fantasyland at the Fantasy Gardens area, or on Main Street.
On the Cruise Line Goofy appears at select times. Check your Personal Navigator for details.