Not sure if it answers, but the documentation says:

$XDG_CONFIG_HOME/git/config
~/.gitconfig

User-specific configuration files. When the XDG_CONFIG_HOME environment variable is not set or empty, $HOME/.config/ is used as $XDG_CONFIG_HOME.

These are also called "global" configuration files. If both files exist, both files are read in the order given above.

The same link also describes the location of other config files (system, local, etc).

Therefore, I guess we don't need a git whatever command to show the paths, as they will always be the ones above.

--

Well, maybe you can make a shell script to check if XDG_CONFIG_HOME exists and show what the actual paths will be:

#!/bin/bash

echo "${XDG_CONFIG_HOME:-$HOME/.config}/git/config"
echo ~/.gitconfig

Ah, so I could do something like

path="${XDG_CONFIG_HOME:-$HOME/.config}/git/config"
[[ -f "$path" ]] && echo "$path" || echo "~/.gitconfig"