I’ve just installed Kontakt 5 and I use Cubase 7.5 as my DAW.
What do I put in the plug-in path for me to get Kontakt to work in 7.5?
It’s been awhile since I installed Kontakt. But as I recall, like most plug-in installations, it suggests a place where it thinks they should go but gives you the option to change that to a place of your choosing. So it is a good idea to take note of that during the install. 
Most likely it is in the Program Files folder on your system disk. If you just poke around there you’ll probably find it easily enough. Or do a search on your system disk for “Kontakt 5.dll” to find the folder it is in. Then use that for your path.
If you haven’t changed the default install path, it’s most likely C:\Program Files\Native Instruments\Kontakt 5.
You can easily check this by clicking on the Start Menu and following the steps I’ve typed above.
Then, if so, that’s your path for Cubase.
You most likely have to click ‘Update’ after you add the path.
Alternatively, you could close the program and reopen it and watch the splash screen to see if it scans for Kontakt 5.