What disenchantable item has fortify enchanting?

You cannot put fortify enchanting onto your armor in Skyrim. This is intentional as it prevents a direct feedback loop. You cannot make a fortify alchemy potion for the same reason.

To clarify, enchanting can boost alchemy, and alchemy can boost enchanting but neither can boost themselves.

Yea, as mentioned you cannot created fortify enchanting gear.

You can however, create fortify Alchemy gear, put it on and then create fortify enchanting potions.

I have my dragonscale light armor at 744, the boots at that point are 327 (same with gauntlets) and my helmet is 354. In addition my deadric swords are at 506 each from using the alchemy/enchanting trick. (It helps to be an orc only because of their perk.)

First you enchant a helmet, gauntlets, ring, and necklace with fortify alchemy. Then make a potion for fortify enchantments. After you do this enchant/alchemy loop repeatedly (about three times) the bonuses won't go above 29%.

Finally enchant some armor, a ring, a necklace, and gauntlets with fortify smithing.

Go to a blacksmith station (I prefer Windhelm; if you mess up and need an alchemy table there's one behind the merchants in The White Phial) drink your potion and make your armor.

Once the smithing is complete I double-enchanted said armor, gauntlets, ring, and necklace with fortify light/heavy armor and fortify one/two handed weapons. (Pick the right one depending on your character build.)

It is time consuming. If you know of the chest in Dawnstar next to the mine it sometimes drops grand soul gems.

(Look up Skyrim cheats for more info. I hope this helps!)