Knol's homepage says a lot about the present state of the project. There's a big empty part called "what's new", a single featured knol that has 1,000 views, while the "most discussed" part doesn't include any knol and the search characteristic no longer works properly.
Knol has been last rationalized in December 2009 and it's clear that the service has been abandoned. Somebody wants to close Knol before it's too late.
If you want to find a list of abandoned Google products, check the copyright notice at the base of their homepage and see if it's been updated. Friend Connect, Google Desktop and Knol still show an old message:.