Copy the unreleased special version of DiscU (the author does not want it to be distributed) to the folder containing your .wud and run the following in a windows command line: discu game.key game.wud with game.key and game.wud being replaced if necessary.

The files will be extracted from the wud's filesystem

Navigate through these folders: [name of extracted wud file without the extension] > ["GM" followed by a title id] > install

Enter the folder of the demo software you want to look at.

Extract the filesystem from the app files by using cdecrypt. Copy cdecrypt (and any dlls required to be in the same directory as the exe) to the folder containing the .app files. Then in a windows command line run cdecrypt title.tmd title.tik

You can now explore the filesystem of the demo and run it in cemu