Civil 3D 2017 paths...

Custom subassemblies using NET
"C:\Program Files\Autodesk\AutoCAD 2017\C3D\Sample\Civil 3D API\C3DStockSubassemblies"

Project reference path for COM programming
"C:\Program Files\Common Files\Autodesk Shared\Civil Engineering 110"

Basic project reference files for autocad NET programming
acdbmgd.dll, acmgd.dll, AecBaseMgd.dll, AeccDbMgd.dll, accoremgd.dll
also files
Autodesk.AutoCAD.Interop, Autodesk.AutoCAD.Interop.Common
all of them found at
"C:\Program Files\Autodesk\AutoCAD 2017"

Basic project reference files for Civil 3D NET programming
Autodesk.AEC.Interop.Base, Autodesk.AEC.Interop.UIBase
found at
"C:\Program Files\Autodesk\AutoCAD 2017\ACA"
also files
Autodesk.AEC.Interop.Land, Autodesk.AEC.Interop.UiLand
Autodesk.AEC.Interop.Roadway, Autodesk.AEC.Interop.UiRoadway
and others
found at
"C:\Program Files\Autodesk\AutoCAD 2017\C3D"

Imported custom subassemblies
"C:\ProgramData\Autodesk\C3D 2017\enu\Imported Tools"

Custom Assemblies dragged to palettes
"C:\ProgramData\Autodesk\C3D 2017\enu\Assemblies"

Original autodesk templates
"C:\Users\LS-W7\AppData\Local\Autodesk\C3D 2017\enu\Template"

Original autodesk ToolPalettes
"C:\Users\LS-W7\AppData\Roaming\Autodesk\C3D 2017\enu\Support\ToolPalette\Palettes"