How to know what are the necessary log files for a backup in DB2?
By default an online backup places the logs necessary to rollforward to the point of the end of the backup inside of the backup file. You can extract the logs from the backup file and then ROLLFORWARD to the end of them. Use the LOGTARGET clause of the RESTORE command to extract the logs to a location (I have tended to restore them to a location other than my logs directory.) Then use the OVERFLOW LOG PATH clause of the ROLLFORWARD command to point the ROLLFORWARD command to the logs you just extracted.

Example:

db2 RESTORE DATABASE TST1 FROM '/db2/backup' TAKEN AT 20150826131633 TO '/db2/data' INTO TST2 LOGTARGET '/tmp/extractedlogs'

db2 ROLLFORWARD db TST2 TO END OF LOGS AND COMPLETE OVERFLOW LOG PATH ('/tmp/extractedlogs')