Are you seeing an error message when you try to execute calibre-debug from the command line that looks like:
'D:\Calibre' is not recognized as an internal or external command, operable program or batch file.
This is due to CMD not being happy with a space in a command string; To get around this, as in @theducks example, wrap the command in "s.
I.e.
do not use D:\Calibre Portable\Calibre\calibre-debug -g
do use
"D:\Calibre Portable\Calibre\calibre-debug
" -g
See
How to Escape Spaces in File Paths on the Windows Command Line for a bit of help.