Most Contiki developers hang out on
contiki-developers mailing list. The list is
a friendly place where good questions asked the right way
typically receive constructive answers.
The Contiki community wiki contains community-provided information about Contiki.
The Contiki source code contains Doxygen mark-up that is used to automatically generate Doxygen documentation.
There is more to read about Contiki, its features and mechanisms, and the Internet of Things.
These two books cover the Internet of Things technologies:
By JP Vasseur and Adam Dunkels.
By Zach Shelby and Carsten Bormann.
Many of the mechanisms behind Contiki have been published in the computer science literature through the papers below. These papers provide technical details and reasoning behind many of the Contiki mechanisms.
There are a number of white papers published on low-power IP technology.
The IP for Smart Objects (IPSO) Alliance has a number of white papers related to low-power IP technology.