If you want to fully duplicate your prefs, copy the whole folder.
I edit "defaults.xml" for recent files, etc. If you have trouble with prefs and need to trash them, this is a good place to start, before chucking them all. Or… remove the folder to a safe location and let Nuendo build a new set… then add old ones as needed (or until you identify what was corrupted).
N6.5x, C4, Halion, UAD-2s (Quad PCI and Satellite), Fireface 800, UR-22, MC Control, Mac(s) 10.9.x, 10.8x, 16G