Hi Johnnys Dog,
That depends on what has caused the deafness. If he has chronic damage to his ear drum and inner ear, probably nothing will restore his hearing. If his ears are plugged up with wax, infection, and pus, then getting all that removed might help. If his hearing loss is just the hearing loss that all older dogs eventually get, then again there is not much that will help.
If he has chronic Cocker ears, with a lot of scar tissue and debris, then having surgery on the ears to remove infected or damaged cartilage might help.
I have seen a few dogs with old age deafness get some of their hearing back with supplementation with anti-oxidants. You could try the prescription diet called B/D, or supplementing with anti-oxidant vitamins, fish oil, N acetyl cystine (N-A-C), SAMe, or other anti-oxidants.
Hope this helps, Rebecca