Reich: Symbolic analyst .
Rifkin: “Creators, manipulators and purveyors of the stream of information that makes up the postindustrial, post-service, global economy.” 
Frenkel et al.: “A knowledge worker as anyone who 1. has a high level of creativity in their work, 2. requires to make extensive use of intellective skills, and 3. makes use of theoretical rather than contextual knowledge.”
Babson College Professor Thomas Davenport has this to say about the concept of knowledge worker:
I certainly think there's a lot of fuzziness, ambiguity, and imprecision about what a knowledge worker is, and it's not a term most managers use easily. They don't say, "Okay, these are my knowledge workers, these are my non-knowledge workers." So despite the fact that the term's been around for a long time, very few people have been comfortable using it as a managerial concept .
Some Occupations/Professions considered as Knowledge Workers
IT and Software designers
Scientists and engineers
1. R. Reich, The Work of Nation: Preparing Ourselves for 21st –Century Capitalism, London, Simon Schuster, 1991.
2. J. Rifkin, The end of Work: The Decline of the Global Workforce and the Dawn of the Post Market Era, penguin, London, 2000.
3 .S. Frenkel, M. Korczynski, L.Donohue, and K. Shire, “Re-constituting Work: Trends towards Knowledge Work and Info-normative Control”, Work, Employment and Society, Vol. 9, No. 4, 1995, 773-96.
4. An interview in Ubiquity Magazine, available online at:
Knol Number 72