You talking about the default location for saved user presets? On my Windows system they're here:
C:\Users\NoelC\AppData\Roaming\Adobe\Adobe Photoshop CC 2014\Presets\Curves
I know that doesn't help you.
Perhaps you could try opening the Image - Adjust - Curves dialog, clicking the little gear icon, and choosing Save Preset. Then you could note the default path from within the Save As dialog...
-Noel