There's a grammar issue here that's confusing the issue. the question of whether knowledge can or cannot be used makes it appear as though usefulness/usability are properties of particular knowledge objects, rather than a function of human interaction with knowledge. I mean, does a rock have use in and of itself? I'd say no, but then again, if I needed to pound a nail and I've lost my hammer, a rock can be used just fine for that purpose. My relation to the rock changes to make the rock useful.
Whether any knowledge object has 'use' in and of itself is debatable. I mean, I 'know' Newton's Laws, but I cannot remember the last time that I 'used' them for any particular purpose. I could use them if I needed to, but... On the other end of the spectrum, I 'know' the theme to Gilligan's Island, and I sometimes 'use' that knowledge to amuse myself and irritate my friends.
Honestly, this question trips over Wittgenstein's 'Language Game #2,' where he demonstrates that knowledge of something is a codification of use that allows cooperative action. Thus if two people are trying to build a wall, they have to find some way of asking for and receiving various needed objects: bricks, mortar, trowels, etc. Thus, knowledge of a 'brick' is not merely tied to an object, but to a class of objects that are used in a particular way within a particular context. Objects that have no use whatsoever never enter into language and so can never constitute knowledge. I mean, image if I said to you: "Well, that's pretty much a blort in a knermil". Unless I explain to you what a 'blort' and a 'knermil' are, and what the relationship between them is, that statement is meaningless. It can be applied to anything, and nothing, and thus cannot be said to express 'knowledge.' Once I explain those terms (assuming I can do so credibly) then we have knowledge, because we can use that phrase meaningfully.