In the US parks it is very rare to find Captain Jack out meeting guests. In WDW he has a daily show in Adventureland; however, he never stops for pictures or autographs. Very rarely if the show is canceled for some reason he may be wandering around the Pirate of the Caribbean entrance or inside the Pirates League.
If you are willing to travel outside the US your chances of meeting Jack increase greatly. He has a regular Meet and Greet on the Caribbean Disney cruises. He is also regularly out in Adventureland at Disneyland Paris. Normally he is around the exit of the Pirates ride or the entrance of Blue Lagoon restaurant; however, sometimes you will find him just wandering around other parts of Adventureland. In Tokyo you can sometimes find him in both Adventureland near the Pirates attraction as well as in DisneySea around the ship located in the Fortress Exploration in Mediterranean Harbor