Windows Server 2012 and Windows 10 came with a lot of changes to the task manager and in some cases the default views have been simplified further than power users and administrators would prefer. One example is by default you only see the total processor utilization and don’t see all CPU cores.
To see all CPU cores right click on the CPU graph and click Change graph to > Logical processors, as seen below:
You will now see the graph of all CPU cores.