alter table

Wait... auditing alter table casts too wide a net?! How often are you doing this? This should be a relatively rare operation!

And you can correlate the alter table audits with created date of partitions in *_objects:

For example:

create table t (
  x int
) partition by range (x) (
  partition p0 values less than (10),
  partition p1 values less than (20)
);

audit alter on t;

conn chris/chris

alter table t add y integer;
alter table t add partition p2 values less than (30);

select uo.subobject_name
from   user_objects uo
join   dba_audit_trail aud
on     uo.created = cast ( cast (aud.timestamp as timestamp with time zone ) at time zone '-7:00' as date )
where  uo.object_type = 'TABLE PARTITION';

SUBOBJECT_NAME   
P2  

But I'm not aware of a way to use audit only for partition maintenance.

If that doesn't help, you could use DDL triggers on alter to capture the event. See https://asktom.oracle.com/pls/asktom/asktom.search?tag=capturing-ddl-changes-on-a-table for an example trigger.