The Wonders of Life pavilion in Epcot is a good choice, followed by Innoventions East (the benches across from that forestry exhibit are comfy and near restrooms). The Land and Living Seas are okay.
In World Showcase, there used to be a small bench inside the Mexico pavilion at the bottom part of the U-shaped indoor ramp that led you down onto the main floor. It's near an air-conditioning vent. It's dark, quiet,cool and out of the way. My brother used to love to rest there while collecting data in World Showcase.
The Stave Church in Norway is cool and dark, but too many people know about it to be a good napping spot. The gazebo in the UK isn't air-conditioned, which is too bad.
In Animal Kingdom, Tusker House or the gazebo behind Flame Tree Barbecue. There's also a nice rest area by the exit to Dinosaur.
In Disney-MGM Studios, try the Commissary. I've not done data collection in the Studios, so I've not been desperate to find ten minutes of shade and quiet. I'll ask my friends what they recommend.
Len