Most documentation is the NAOqi 2.8 reference documentation, specifically the Developer Guide which contains tutorials and a complete API reference.
The Aldebaran Developer Center has content related to application development, such as:
You can also search the nao-robot tag on StackOverflow, and ask questions to the community over there.
The software tools (Choregraphe and Python SDK) and the SDKs can be found on the NAO6 support website.