Where does console output go I'm trying to debug a Python script by placing a print("foo=" + foo) statement in my code.

But where does the output appear?   

It doesn't appear on the Python Console, and it doesn't appear on the area that appears when you drag the lower edge of the infobar downwards (what is the name for this area? My script errors show up in red here.)
It's printed to the system console. If it's not opened, go to Window &gt; Toggle System Console.
Note that this option is only available on Windows. On other OS, start Blender from a terminal.
See here: https://docs.blender.org/manual/en/latest/advanced/command_line/introduction.html
You may also use this script:
Is there anyway to make blender print errors in the UI?