I bought my friends old iPad when he got a new one - how do I transfer ownership, etc?
There is no transfer of ownership per se.
Restore the iPad with iTunes as a new iPad if your friend did not do this prior to the sale.
The standard one year warranty and the AppleCare extended warranty remains with the device.
You may want to visit https://supportprofile.apple.com/
and see if you can register it under your name.
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