Full Idea
The failure of the KK principle is not news. The standard counterexamples involve knowing subjects who lack the concept of knowledge, or have not reflected on their knowledge, and therefore do not know that they know.
Clarification
The KK principle is knowing that you know
Gist of Idea
Knowing you know (KK) is usually denied if the knowledge concept is missing, or not considered
Source
Timothy Williamson (Vagueness [1994], 8.2)
Book Reference
Williamson,Timothy: 'Vagueness' [Routledge 1996], p.225
A Reaction
There is also the timid but knowledgeable pupil, who can't believe they know so much. The simplest case would be if we accept that animals know lots of things, but are largely devoid of any metathinking.