If I wanted to report a bug, how could I find my MacTeX version via command line?
You could try
cd /usr/texbin pwd -P
Otherwise, you can see the version through MacTeX's preference pane, which is automatically added to System Preferences upon installation.
From the MacTeX Support Mailing List:
in Terminal. The first of many lines it returns gives the TeX Live version which is also the MacTeX version. E.g. I get
pdfTeX 3.1415926-2.4-1.40.13 (TeX Live 2012) ...
since I'm using TeX Live 2012 and therefore MacTeX-2012.
Find the installer "MacTeX-2xxx.pkg" and get info. The version number is listed.