if you talk about extracting the files from the wud image, I don't know.
if you talk about dumping a disc, you need to be able to read it, but the PC can't read the WiiU disc so neither the emulator.
the WiiU can do it, there are different homebrew to dump a disc.
you can dump it to full 23/25GB wud format with wuddump, or extract only the encrypted app files with disc2app.
https://gbatemp.net/threads/the-different-wiiu-games-formats-and-how-to-convert-them.449212/
look at the first 2 links.
if you want to extract the wud image content to encrypted app or decrypted files (file system, with files and folders like the one used by loadiine, or if you want to mod a game) then you can use some tools, no need of Cemu.
look at the Wud decrypters / Disc extractors / content Decrypters sections.
if you don't want to use the CD and the console, you can use CDN downloaders.
there's also a way to get individual files from CDN, directly in encrypted or decrypted format, with JNUSTool. no need to dump or get the full game if you only want to extract one file.
obviously, you'll need the game's titlekey for cdn method if you want to decrypt and get only few files.