How to specify which editor is used when editing posts with WP-CLI?

I thought the command must be typed like so:

$ export EDITOR=emacs; wp post edit 1

Which is exactly how it’s working for me on my 10.14.5 macOS right now. And on Linux as well.

Maybe something is misconfigured on your Mac. Or @alias is interfering. Can you try to rerun that command without @alias or on a fresh macOS installation?