There is no such earring that gives +6 wis, at least not one that's player made. Jasper and platinum make a +6 RING, but that's a finger item, not an ear item.
The most wis a player made earring (pre-PoP anyway, not sure about PoP/LoY recipes, but so far every new jc recipe I've seen are all finger items, not ear) has is 4; the imbued plains pebble and imbued ivory gold earrings have this much if you follow the right deities (Karana and Tribunal respectively).
I had the 2 wis version of these things for a while and I was pleased when I finally found someone who had a pair of gold ones they wanted to sell.
I'm a Barbarian Shaman and I must say they're nice to have. I'll admit everyone is all the buzz about forest loops but I personally don't like paying that much for an item with the same stat I want plus a few others. ;-)
Also as a Bar Shaman, I will be upgradeing to imbued ivory gold ear rings, so if you want to know how to get a little more wis in the ears, look into thoes.