If knowledge is fact based, then a machine can know. Because machines have the power to reproduce material stored in their memory, it could be said that they know the facts and are capable of using them. All existing facts could be converted into digital form and imputed into a machine in any language. Since knowledge can change based on acquisition of new facts, more facts could be continuously entered so the claim that knowledge may be factual can be satisfied.
Humans use information from different areas of knowledge to make a reasonable guess that can be proven over time. For example, the existence of black holes is unproven but humans assume they exist from looking at images of distant stars having materials extracted from them by apparently large, super-gravitational forces. Machines, however, are unable to investigate ideas due to their limited reasoning abilities. They cannot speculate that the existence of a black hole may have an indirect proof. If knowledge were more than just purely factual statements, then a machine would fail to know.
Can a machine differentiate between right and wrong with its limited understanding of human nature?
References: Dave Harris and Colleagues. "Plato 's Metaphysics." http://www.arasite.org/plato.html