Roger,
Cod isn't a great choice for the smoker IMO. But, if you decide to try it, think under smoke and the mildest wood you own. The flavor of cod is so light and delicate that it just gets over powered very easily.
I think Dave is spot on> " The flavor of cod is so light and delicate that it just gets over powered very easily. "
I've done Cod loins on the grill as follows...
Maple chips in a smoke box and get them smoking
Lightly brush the loin with melted butter and season with lemon pepper salt.
Bring the grill to 350 degrees and grill for about 10 minutes. then start checking the loin for flaking. when it flakes easily they are done.
I get a light smoke flavor without overwhelming the taste of the cod. Hope this helps.