IF you have installed Tiddlywiki globally as a node.js package, you can invoke it with just "tiddlywiki" in the command (which it looks like you have done).
So, when starting the server on either device, you can have the "command line directory" set to anything you want if you pass the full (or relative) path from there to where your wiki is located. The below would be equivalent if your command prompt reads "
C:\Users\Fred> " as it does in your example.
tiddlywiki '../../Wikis/mynewwiki' --listen
OR
tiddlywiki 'C:/Wikis/mynewwiki' --listen
If you do give the full path to your SD drive, then you are giving node.js permission to actively read/write from the SD card as your wiki changes. It might be better on your PC to have the wiki in a folder on your hard-drive, and then sync to and from the SD card when you want to sync the copies.
I use the Free File Sync app @
https://freefilesync.org/ to synchronize a set of QWikis between 2 PCs, by syncing to the Wikis folder to an external HDD, and then syncing that Wikis folder to the other PC's hard-drive.
Best,
Joshua F