The QiSDK documentation contains all API references and some tutorials.
The Aldebaran Developer Center also has a lot of documentation, including
There are also useful examples and libraries on the Softbank Robotics Labs Github Repository.
You can also find search the Pepper tag on Stack Overflow.
Most documentation is the NAOqi 2.5 reference documentation, specifically the Developer Guide which contains tutorials and a complete API reference.
You can also search the Pepper 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 Pepper support website.