Skencil's documentation is included in the stable source archive and the rpms but it's also available online. There a two documents:
The User's Guide contains an introduction to the user interface and the concepts of Skencil and an introduction to user scripts.
The Developer's Guide describes Skencil's internals and is mainly interesting for programmers who want to contribute to Skencil, but is also important for writing Scripts.
Some sections of the Developers Guide may also be interesting for other Python programs, like the section on the undo mechanism.
Frédéric Toussaint, Yves Ceccone and André Pascual have written some new user documentation. It is inteded for use with young students in France and is therefore written in French, but there's a rough English translation as well.
The site also has a quite extensive collection of Skencil cliparts.
Tobias Hilbricht has started on a German user manual.
The article in the November 1999 issue of LinuxFocus is a review as well as an introduction and tutorial of Skencil.