Have you found it? Easy way is to open Finder -> go to folder -> ~/Library/Application Support/Bitcoin
The ~ tells it to go to your user directory.
Right, in the case of MacOS (a unix flavor) that translates by default to /Users/<username>. So you could also check:
Now to figure out a nice and simple way to backup / transfer the contents of that directory.
Personally, I would suggest backing up the entire thing (for backups) just to be safe. EG., you're backing up the client's current block download too. I've just tried mixing and matching block downloads and wallet.dat files. Doesn't work, even though I thought it should.
But that directory can get pretty big with all the block downloads, etc...