Ok. Found the article. The article focuses mainly on "Visibility" and the long term importance of visibility.

http://www.mcgeesmusings.net/stories/2002/03/21/KnowledgeWorkAsCraft.html

"One thing that differentiates knowledge work today from other craft work is that, except for final product, knowledge work is essentially invisible."

The following sentence is interesting.

"As craft work, knowledge work fits more into apprenticeship learning models than in conventional training approaches. "

It would be interesting if someone could create a scale for different types of work and establish some kind of "Knowledge Work" index. If a job is suited for apprenticeship can we conclude that is knowledge work.