Kokanee will have a much longer rakers (not sure about wider but not arguing, due to being plankton sifters). As opposed to short and stubby rakers (due to being meat eaters), that is the defining moment between kokanee and coho/king if you ask me (agreeing with Smalma). Picture doesn't define this, so my next questions would be.....
are there spots on the bottom of the tail or only on the top? Tough to tell in pic, appears no spots on bottom and minimal silver in tail.
if only on top, I would lean Coho.
if on top and bottom, I would be convinced King.
The Cadual Penducle "can" also be a definining characteristic between coho and king. The Coho's will actually be wider as it goes into the tail. Meaning the penducle (silver part) tapers down below the line of the body between tail fin and anal fin. A king would extend almost straight back into the tail on a straight line, no drop. A coho drops down creating a wide cadual penducle.
Based on the cadual penducle, and the fact that I cant see spots on tail and just a little bit of silver on the tail (kings also tend to have more silver in tail)
Coho is my answer as well.