Check how many CPUs visible offline & online

--how many CPUs is SQL Server actually using

select cpu_id,scheduler_id,is_online,status from sys.dm_os_schedulers where status = 'VISIBLE ONLINE'

--how many CPUs are not being used

select cpu_id,scheduler_id,is_online,status from sys.dm_os_schedulers where status = 'VISIBLE OFFLINE'

--how many CPUs an instance can see

select cpu_count from sys.dm_os_sys_info