Usually, there is no need to directly access most of the tables. Nevertheless, some of the tables can be interesting:
DBRSAPPLY_CONFLICT_LOG
List of conflicts encountered, including failing SQL.
DBRSAPPLY_CONFLICT_HANDLERS
Conflict handler settings. Note that the key is object id on source database.
DBRSAPPLY
Includes last commit SCN (current_scn), so it can be used to monitor apply progress if SNMP or log monitoring is not an option.