How does one access Texinfo manuals (commandline example would be: info gdb) from within emacs? This does not appear to be M-x info as I don’t see gdb in the menus)
Is there a list, perhaps, which has paths to info manuals that I need to check to make sure emacs has the same locations to look for these manuals as the info command?
Assuming you've installed the info docs, eg. gdb-doc package or whatever, you should be able to see the info page with M-x info-display-manual gdb.
As far as the lookup path, you could check Info-directory-list from emacs to see if it is getting initialized properly from your INFOPATH.