This is another over complicated issue (thanks Apple) but the following advice should help in locating the log.

Firstly you need to identify your home folder, usually in Finder there is an option for "Go -> Home" in the finder menu. This will put you directly into your home folder.

Inside the home folder there is a Library folder that has the hidden attribute set. This means you cannot see it unless you enable hidden files.

Seeing hidden files is achieved in different ways for different OSX levels and we suggest googling your specific osx level and "displaying hidden files" to get the correct advice for your OSX level.

For High Sierra and later the process has been simplified and you can within the finder window press CMD + SHIFT + .

Once you can see hidden files then inside the Library folder there is a Logs folder and inside that a Unity folder. 

Inside the Unity folder is the Player.log file which is the log for the sim.

The total path is therefore /Users/your home folder/Library/Logs/Unity/Player.log