Aww...he sounds like my Scottie when he was a puppy - picky little one!
Is he eating his kibble meals though? Everything else is checked out to be good and normal by the vet? I just know with Scottie, it took him a while to become interested in food and treats.
For my two, I currently give them dehydrated lamb lung, dehydrated sardines, and freeze-dried Stella & Chewy's meal patties as treats (broken into small pieces of couse). Try to stay away from treats that are heavy in liver. If there's too much liver content, pups have a tendency to get upset stomach due to the high fat content.
If for now your baby isn't interested in treats, try just using praise for training (i.e. high pitched "ooooooh good boy!!!"). Or toys. Whichever they are interested in.