I start off with the axiom
Knowledge is True and Justified Belief
and take it from there.
However, in testing a theorem, would the realization of skills acquisition be considered a lemma to the original proof, and thus be a concrete epistemological truth -- by direct observation -- of the skill itself? Hence, learning can be proven, with the side-effect of potential practicability thereto! And thus you KNOW a new skill -- like Perl Programming!
"Perl. There is no substitute."