Via CLI
I believe Microsoft Word stores these preferences in this file: ~/Library/Preferences/com.microsoft.Word.plist. You could use the plutil to view the contents or a text viewer CLI tool such as cat, more or less. .plist files are merely a variant of XML files.
$ plutil -p ~/Library/Preferences/com.microsoft.Word.plist
I'd look in this file for something related to "default" and "save".
Via GUI
If you prefer doing this through the GUI the official Microsoft Office docs show where you'd do this in this doc titled: Save a file in Office for Mac.