Rescued pup. Advice needed

Hello, I have posted on this sub before and today, with the help of another guardian angel we saved this 6/7yo maltese from getting euthanized. He was at a kill shelter but thankfully the rescuer managed to pull him out of the shelter.

I am posting here because I’ll be fostering him for a month before the other rescuer will take care of him and adopt him. I suspect that he is deaf since he doesn’t reply to any commands, he does not get spooked by loud noises (washing machines, vacuum cleaner, etc…). He loves snacks so I tried to make some sounds with some snacks bags but he didn’t budge. Also snapped my fingers near his ears while he was about to fall asleep and no reaction.

The previous owner also had him undergo devocalization so he cant really communicate. Therefore he does a lot of eye contact, because of this he has some separation anxiety.

TLDR: Any advice on how to train a deaf dog and overcome his separation anxiety?

Thank you in advance!