MAC SSD (or HD depending): Users/Shared/NI Resources/image/ 'Instrument name'
The artwork existed in the following directory, open this in Finder window: nicnt file expected to find it, hence no display.
The artwork existed, but it was not where the. nicnt file was setup to find it elsewhere. I had already installed library and library worked (included GUI artwork and interface once loaded), reinstalling didn't fix the missing library wallpaper, an there was no 'wallpaper.png' file in the directory, as the.
In case this is helpful to someone else, I had some Kontakt libraries not displaying the library instrument wallpaper (just showing grey background), the below worked for me (on Mac):
