AP kog'maw viable or not??

Could be, depends on the elo honestly, though the question mounts, why not just Xerath?

it does work, he just has a harder time early against the more mobile mids(lb kat akali zed etc.) so i recommend taking barrier or exhaust but yes it does work the best parts are his e and r if you cant hit those consistantly you cant do much

Viable? Sure. Will you see him in an LCS game? Only with very specific comps. He needs a lot of protection, and his lane phase is pretty vulnerable as a result. At least when he ADCs he gets a support.

If you Rush tear, into Sorc boots, Scepter Torment, then yeah. Completely viable. I love it. It's really bad in this meta though. :c