I’ve had limited success grafting cornelian cherries on to my two 6 year old seedling trees - less than 10% of the grafts that I’ve attempted have been successful, but I do have four takes. All have been veneer grafts with scions slightly smaller than pencil diameter and about 2 to 3 inches long with at least 2 nodes. I successfully grafted them in early spring during flowering and or just as the leaf buds are starting to break.
Initially I tried whip-and-tongue grafts with no success, and later I did bark grafts after the bark started slipping. Those grafts have served me well on pears, apples, persimmons, jujubes and pawpaws, but I didn’t have any success with them on cornelian cherries. I suspect chip budding might work as well, but I haven’t tried it yet. It seems that grafting to the tips of branches isn’t as effective as grafting lower down and then removing the tips above the graft once it has successfully taken.
I was very disappointed with the fruit quality of my seedlings - they didn’t compare favorably with the fruit I’d previously tasted. But this last year, the fruit were significantly better. So I mention it only to say that the fruit can improve as the tree ages.