If you've not figured it out already, I suggest you to follow this tutorial: https://gbatemp.net/threads/jnustool-unofficial-gui-mod.445962/
Using this tool you can find the base Wii U VC game (in RAW/decrypted format) listed in the compatibility list. The game you want to play (and inject) has to be an n64 rom.
Using this tool you can find the base Wii U VC game (in RAW/decrypted format) listed in the compatibility list. The game you want to play (and inject) has to be an n64 rom.