The challenge was simple... can SQL be used to compare the contents of two spooled files? The solution follows...

Compare the contents of two spooled files.sql

-- ========================================================================
--
-- Subject: Comparing two spooled files
-- Author: Scott Forstie  
-- Date  : December, 2021
--
-- IBM i Services used : OUTPUT_QUEUE_ENTRIES_BASIC, SYSTOOLS.SPOOLED_FILE_DATA
-- SQL language features used: CTEs, Exception joins, Union, and row_number()
-- ========================================================================

-- ========================================================================
--
-- My two, most recent, QPRINT spooled files
--
-- ========================================================================

select job_name, spooled_file_name, file_number
  from QSYS2.OUTPUT_QUEUE_ENTRIES_BASIC
  where USER_NAME = Session_user and spooled_file_name = 'QPRINT'
  order by CREATE_TIMESTAMP desc
  limit 2;
stop;

-- ========================================================================
--
-- My two, most recent, QPRINT spooled files (CTE style)
--
-- ========================================================================
with top_two_spooled_files(rn, jn, sfn, fn) as (
       select row_number() over(),job_name, spooled_file_name, file_number
         from QSYS2.OUTPUT_QUEUE_ENTRIES_BASIC
         where USER_NAME = Session_user and
               spooled_file_name = 'QPRINT'
         order by CREATE_TIMESTAMP desc
         limit 2),
     first_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 1),
     second_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 2)
  select *
    from first_spooled_file
  union all
  select *
    from second_spooled_file;
stop;

-- ========================================================================
--
-- The contents of my two, most recent, QPRINT spooled files
--
-- ========================================================================

with top_two_spooled_files(rn, jn, sfn, fn) as (
       select row_number() over(),job_name, spooled_file_name, file_number
         from QSYS2.OUTPUT_QUEUE_ENTRIES_BASIC
         where USER_NAME = Session_user and
               spooled_file_name = 'QPRINT'
         order by CREATE_TIMESTAMP desc
         limit 2),
     first_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 1),
     second_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 2)
  select jn, sfn, fn, p.*
    from first_spooled_file, lateral (
         select *
           from table (
               SYSTOOLS.SPOOLED_FILE_DATA(
                 JOB_NAME => jn, 
                 SPOOLED_FILE_NAME => sfn, 
                 SPOOLED_FILE_NUMBER => fn)
             )
       ) p
  union all
  select jn, sfn, fn, p.*
    from second_spooled_file, lateral (
         select *
           from table (
               SYSTOOLS.SPOOLED_FILE_DATA(
                 JOB_NAME => jn, 
                 SPOOLED_FILE_NAME => sfn, 
                 SPOOLED_FILE_NUMBER => fn)
             )
       ) p;
stop;

-- ========================================================================
--
-- Return any differences between these two spooled files
--
-- ========================================================================

with top_two_spooled_files(rn, jn, sfn, fn) as (
       select row_number() over(),job_name, spooled_file_name, file_number
         from QSYS2.OUTPUT_QUEUE_ENTRIES_BASIC
         where USER_NAME = Session_user and
               spooled_file_name = 'QPRINT'
         order by CREATE_TIMESTAMP desc
         limit 2),
     first_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 1),
     second_spooled_file (jn, sfn, fn) as (
       select jn, sfn, fn
         from top_two_spooled_files
         where rn = 2),
     first_spooled_file_data (jn, sfn, fn, ord, data) as (
       select jn, sfn, fn, p.*
         from first_spooled_file, lateral (
                select *
                  from table (
                      SYSTOOLS.SPOOLED_FILE_DATA(
                        JOB_NAME => jn, SPOOLED_FILE_NAME => sfn, SPOOLED_FILE_NUMBER => fn)
                    )
              ) p
     ),
     second_spooled_file_data (jn, sfn, fn, ord, data) as (
       select jn, sfn, fn, p.*
         from second_spooled_file, lateral (
                select *
                  from table (
                      SYSTOOLS.SPOOLED_FILE_DATA(
                        JOB_NAME => jn, SPOOLED_FILE_NAME => sfn, SPOOLED_FILE_NUMBER => fn)
                    )
              ) p
     )
  select a.jn, a.sfn, a.fn, a.ord, a.data
    from first_spooled_file_data a
         left exception join second_spooled_file_data b
           on a.ord is not distinct from b.ord and
             a.data is not distinct from b.data
  union all
  select b.jn, b.sfn, b.fn, b.ord, b.data
    from first_spooled_file_data a
         right exception join second_spooled_file_data b
           on a.ord is not distinct from b.ord and
             a.data is not distinct from b.data
 order by ord;