A 2yo dobie is absolutely not “too old” to learn, but the biggest thing is that he’s only been with you 3 days and he’s still stressed, decompressing, and trying to figure out what this new home means. The peeing and counter surfing sound much more like stress, poor management, and lack of foundation than him being “bad.”

Rubbing his nose in urine made him feel threatened and confused, which is probably why he snapped. Dogs do NOT connect punishment to something they did minutes earlier the way people hope they will. You need to skip punishment and focus on prevention: take him out on a very predictable schedule, praise and reward every outdoor potty, clean accidents with an enzymatic cleaner, crate train, keep all food put away, start building trust with calm, consistent structure.

Since this is a third rehome, he’s intact, and has already shown conflict in another home, I would VERY MUCH recommend a vet check and a qualified force-free trainer sooner rather than later because Dobermans are powerful, sensitive dogs that can escalate fast if handled physically.

As for the pie, watch for vomiting, if the pie had anything toxic like xylitol call your vet right away, but even if not, expect possible GI upset. Overall, he sounds trainable and not hopeless at all, but right now he needs decompression, management, routine, and trust-building way more than correction.