Documentation is provided for v3.1 to v3.4, in separate places. Each major release of Kohana v3.x has independent documentation.
Documentation is also included in the userguide module in all releases.
Once the userguide module is enabled in the bootstrap, it
is accessible from your site with /index.php/guide (or
just /guide if you are rewriting your urls).
Kohana v3.x is self-documenting when the userguide module
is enabled. If you follow the documentation conventions when developing
your application, your documentation will grow with your application.
The Kohana user community may be able to help you find the answer you are looking for.