Is it 'wet' your appetite or 'whet' your appetite?

The correct form in "to whet your appetite".

"Whet" means to hone or to make more keen or stimulated, whereas "wet" means to cover or soak with water.

a whet "wet" rock is used to sharpen knives.

the stone or rock is actually wet with water or oil to lubricate & cool the material bing sharpened