We can use below script to find the workflow service log file name and location.


set linesize 100; 
set pagesize 200; 
set verify off; 
column MANAGER format a15; 
column MEANING format a15; 
SELECT concurrent_queue_name manager, fcp.last_update_date, fcp.concurrent_process_id pid, meaning, fcp.logfile_name 
FROM fnd_concurrent_queues fcq, fnd_concurrent_processes fcp, fnd_lookups flkup 
WHERE concurrent_queue_name in ('WFMLRSVC') 
AND fcq.concurrent_queue_id = fcp.concurrent_queue_id 
AND fcq.application_id = fcp.queue_application_id 
AND flkup.lookup_code=fcp.process_status_code 
AND meaning='Active';