The Memo to Users for the upgrade (aka the upgrade documentation) should cover all of the changes made.
What I find strange though is that IBM does't usually break anything during upgrades (at least without covering it in the memo to users).
What problems are you having. Can you provide a sample?
Based on the sample, couldn't you do:
FROM "JFPMTPRDD".T1HEAD2L head
INNER JOIN "JFPMTPRDD".PROD1P prod ON trim(fas.IDPROD)=trim(prod.IDPROD)
INNER JOIN "JFPMTPRDD".MSTRFA1P fas ON trim(head.FASID)=trim(fas.FASID)
INNER JOIN "JHFINLI31A"."CFMAST" cfiloan ON trim(head.MFCODE) = cfiloan.CFCIF#
LEFT JOIN "JFPMTPRDD".TMSG01P errMsg ON (head.MSGCOD = errMsg.MSGCOD)
It might be that the query is looking for all of the joins defined.