Where can you view the client licensing mode of a Windows 2008 Server?

Try LicMgr.exe

Use the following also:
1. Go into  Server Browser tab.
2. Choose  domain and server.
3. If  icon appears as a computer with a file and no CRT, then the computer is running in the Per Server mode. If the icon displayed is a computer with a file and a CRT, then computer is running in the Per Seat mode. Double-clicking on these icons allows you to change the licensing mode and edit the product properties. 

Alternate Method of Determining Licensing Mode
An alternate way of determining which license mode a computer is running both locally and remotely is to do the following:

1. Select the Products View tab.
2. Select the Product from the list.
3. Select the Server Browser tab.
4. Select the computer from the list. It displays the licensing mode the computer is running in specific to this product.

LicMgr.exe does not exist in the Windows or System32 directory. I assume that is where you are expecting me to find the tabs you reference. I am running Windows 2008 Server R2

Have a look at this link: http://www.windowsnetworking.com/articles_tutorials/Windows-Server-License-Manager-Script-slmgrvbs.html

I would leave the question open.

Here is the correct answer there is no licensing module in Windows 2008 server this has removed by MS. You must keep copies of all licenses instead of placing them into the server.

There is still a Terminal Server licensing module where you must install TS Cals but you don't have to keep track of Server CALs in a licensing module.

The only thing I would add is that if you have a MS Select or Enterprise Agreement, your licenses are tracked by the MS Volume Licensing Web site. I dont see the need to keep copies especially if you already maintain a PO database should MS fail to track any of your licenses properly.