How to get the trace file:

The following query returns the Trace file path location for a particular Concurrent Request and Pass the request id as parameter.

SELECT distinct
    req.request_id
    ,req.logfile_node_name node
    ,req.oracle_Process_id
    ,req.enable_trace
    ,dest.VALUE||'/'||LOWER(dbnm.VALUE)||'_ora_'||oracle_process_id||'.trc' trace_filename
    ,prog.user_concurrent_program_name
       ,phase_code
    ,status_code
    ,ses.SID
    ,ses.serial#
    ,ses.module
    ,ses.machine
    FROM
    fnd_concurrent_requests req
    ,v$session ses
    ,v$process proc
    ,v$parameter dest
    ,v$parameter dbnm
    ,fnd_concurrent_programs_vl prog
    ,fnd_executables execname
    WHERE 1=1
    AND req.request_id = '&request_id'
    AND req.oracle_process_id=proc.spid(+)
    AND proc.addr = ses.paddr(+)
    AND dest.NAME='user_dump_dest'
    AND dbnm.NAME='db_name'
    AND req.concurrent_program_id = prog.concurrent_program_id
    AND req.program_application_id = prog.application_id