How do I evolve sunkern?

You need a sun stone and you get a sun stone in mossdeep city or wild pokemon

You need a sun stone which is on six island somewhere.

Well, you need a sun stone. If you used it on Gloom for it to evolve into a Bellosom or however you spell it, you're out of luck because you can only get one sun stone in the game. Try trading a Pokemon holding the sun stone from a different game. And it's rumored that some Solrock (Meteor Falls) holds sun stones, but 1. I haven't found that to be true, and 2. That's a rumor for ruby. But, if you didn't even retrieve the sun stone yet, you get it in the space station place in Mossdeep. On the first floor, there's an old man. Talk to him and he'll give you the sun stone.

You need a sunstone to elvove him

A guy in the space station and wild Solrock.
;)

If you talk to the sailor inside the space station at Mossdeep,he will give you a sun stone.If you use this sun stone on Sunkern,it will evolve.

1. Get the sun stone from mossdeep
2. Use the clone clith to get 2 stones
3. Use a sun stone on sunkern to evolve him
4. You'll still have a sun stone left for gloom