Is there a list of all iOS features available for iPad 2?
Welcome to iMore! There really isn't much out there highlighting the features of iOS 9 on iPad 2 because it's such an old device. Perhaps it would be more helpful to talk about what ISN'T available on the iPad 2:
Split View, Slide Over, and Picture-in-Picture multitasking
The new Spotlight screen, predictive Siri, and third-party Spotlight search
Public transit directions for Maps
Handoff features in Continuity
I would not be surprised if Apple announces no iOS 10 support on iPad 2. We will know soon.
to give credit where credit is due, I found the above information here