To be honest im not 100% sure, but i had caught wind last year that he had a 40" vertical. Not sure how accurate that was, but considering theres several videos ive seen of him having to duck his head slightly to keep from hitting it on the rim id say 40" is pretty close.
Edit: According to Coach Vermillion in the article they have in the Kingsport Times News this morning, he claims that hes only got a 47" vertical when they try to gauge him in practice but he swears it goes to 50" when it's gametime. Surely Coach got confused....47" vertical?!?!