I would like to add AdomdClient Reference to a C# Project, but it is not in the reference list. The Client is listed in the assembly Folder C:\Windows\assembly.
On the machine is SQL Server 2012 installed.
If you need it in your solution, and you know the location (as you indicated, in c:\windows\assembly), right click your References node in the solution explorer in Visual Studio, then click "Add Reference." Click the "Browse" button, find your DLL file, and click "Add" in the dialogue box. It should show up checked in your reference list. You should then be able to reference it in your C# file.
If you don't have the ADOMD client DLL file handy, download it from the Microsoft SQL Server 2012 Feature Pack (http://www.microsoft.com/en-us/download/details.aspx?id=29065). Click "install instructions" and look for "Microsoft® SQL Server® 2012 ADOMD.NET"