Below is the script to find the os server process id of a SID.

set lines 123 
col USERNAME for a15 
col OSUSER for a8 
col MACHINE for a15 
col PROGRAM for a20 
select b.spid, a.username, a.program , a.osuser ,a.machine, a.sid, a.serial#, a.status from gv$session a, gv$process b 
where addr=paddr(+) and sid=&sid;

SEE ALSO – Get sid from ospid