~ is the home directory, not the root
That should be /home/username/.digitalcoin
Yep, this. Some altcoins will use capitalization in the directory path, e.g.,
~/.MemeCoin
If you run the QT or daemon once it will create the relevant directory and then you can just replace the "empty" wallet.dat with the one you are copying over.
The only coin I've encountered that doesn't follow this convention for the location of wallet.dat is a real oldie: fairbrix. Instead, only the configuration file (fbx.conf) goes inside ~/.fairbrix and the wallet.dat goes inside ~/.fairbrix/data. It's possible a few other ancient coins from that era also differ in their file structure.