Source Documentation
From K-3D
Source code documentation
You can browse through source-code documentation generated nightly with Doxygen at:
http://www.k-3d.org/docs/doxygen
Python object model documentation
You also can browse the python object model generated nightly with epydoc at
http://www.k-3d.org/docs/epydoc/
UML docs
There's no UML diagram for K-3D, though there exist several programs that import C++ :
Feel free to give them a try.