Can somebody help me tell how to know that server has how many per cpu core available?
Your post tells us that you have two Xeon E5-2660 processors and that they were manufactured by Intel.
Perhaps you can learn everything you want by going to Intel's web site and finding all the technical information from them.
An alternative method to get information would be to use a Google search for something such as "intel xeon e5-2680 cores" or you could go to some online retailer that sells such hardware and see how they describe them.
As for "How many are available" ?
ALL the cores will be available, to the full extent of whatever the OS or your applications are designed to use CPU cores, unless you have done something to disable processor cores.