I am considering upgrading my box to a dual 8-core CPUs.  Will Sonar Platinum make use of 2nd CPU and additional cores?  If it's not evident, I am hardware illiterate--I was told to make sure my DAW would support this before I upgrade.
 
Thx
Bruce

Depends on the OS. SONAR will use all the CPUs and cores the OS supports.

Yes, Sonar will use all the cores. Dual-socket machines need the Pro version of Windows (7 , 8, 10) to allow both sockets to be engaged. I run a dual socket Mac Pro (2x six cores = 12 cores, 24 logical processors) using Win7 Pro and Win10 Pro, and macOS Sierra.

Great!  Thanks very much!

Your DAW will run great! More cores and hyperthreading is mm-mm good.
 
One important caveat is that some plug-in licensing mechanisms will break if you change too much hardware. PACE/iLok is one I can think of. Not the dongle, but the service that runs on the computer itself.
 
I did a motherboard swap in my main DAW system and didn't unregister my PACE/iLok plugs first and had to contact both iLok and some of the plug-in developers to get some of my licenses back. So if you have any plug-ins that are licensed via that method, I would suggest you unregister them temporarily, then re-register them after the CPU installation is completed and your system is back up and running.

Follow-up:   I moved up to dual E5-2667 CPUs and 96GB RAM.  Sonar Platinum and I are very happy with the performance.  I did have to upgrade my Windows 10 Home to Pro.