The monThread monitor table includes information about all threads in SAP ASE.
select count(*) from monThread
However, many threads reported from this query are from syb_blocking_pool, which do not require much CPU and need not be considered for resource planning.
Subsequent runs of the same query will provide exact results, unless some threads are transitioning their states.
During resource planning, pay particular attention to the number of query processing, or engine, threads, that run user queries. Determine the number of query processing threads by issuing select count(*) from monEngine, select count(*) from sysengines, or by adding the thread counts for syb_default_pool to the thread counts for any user-created thread pools.
sp_sysmon displays the amount of CPU resources each thread consumes. See Performance and Tuning Series: Monitoring SAP Adaptive Server with sp_sysmon.