Brining pork belly?

You need to understand what " brining " is.
A pork belly is fat loaded, and water + sodium molecules can't pass through fat.
Plus, why on earth would you want to brine a meat that you wish rendered of fat?

Yes, I know that millions do it, I'm just asking you to think about why.
hTH

If he has made bacon before he is familiar with understanding the process.

I think the confusion comes from the terminology used in the post. While making bacon some people call it a cure while others call it a brine because it is a solution of water, salt, and sugar. If it has a curing agent (pink salt) it is a cure, if you make bacon without a curing agent it is merely a brine. many stores sell uncured bacon here in the US including Trader Joes....

I guess it would be helpful if "GermanyCharcuterie" would explain what he is trying to make with the apple brine and apple wood smoking process....

Also see this thread.... Smoking Pork Bellies