I note the -d (enable debugging), but it's not pointing anywhere, because
it doesn't take an argument. Specifically, it will *never* show you a manual
page; even if it finds the page (which it doesn't in your case), it just prints
out the command it would have used to display it.
In your case, you've asked it to turn on debugging, format the manual page
"/usr/share/man", and then give you the manual page for "man" in
section 8 of the manual.
The manual page for "man" is in section 1 of the manual, so man
(correctly) tells you you can't find it in section 8.
Try a less convoluted command:
$ man man
and if that fails,
$ man -d man
For what it's worth, what you think -d did appears to be done by -M,
but it shouldn't be necessary anyhow. (Remember that setting a manpath
with -M or $MANPATH *replaces* the system one, rather than augmenting
it.)
Cheers,
-Rich