I had a chance to pet some young Galapagos tortoises in June. They go off to Never-Never Land if you scratch the jaws and neck. They can learn certain associations, though. Most notably, if you always drop food into the cage, the snake will associate opening the cage with the coming food and eventually bite the first thing that comes in when the lid opens, including your hand. A lot smarter than snakes.
Turtles can learn a lot of little things and routines, given enough time and food rewards.
Turtles are creatures of habit - they don't like change at all. The latter can result in a turtle that will follow you around the room or the yard in order to coax you into scratching its head or giving it food. One person informed me, that his Wood Turtles are potty trained, will walk up to the refrigerator if they are hungry, and go to the bathroom and sit in front of the tub until they get the bath they desire. All my water turtles know that food comes from the kitchen, and they also can discern fingers from food quite easily, if they want to. Henry learned that the nozzle on the garden hose will be either bright orange or bright yellow.