How can I find out which tables use reference partitioning from the Oracle data dictionary?
To get a list of partitioned tables that have at least one referencing partitioned child table the [dba][all][user]_part_tables and [dba][all][user]_constrains data dictionary views, depending on the privileges granted, can be queried:

create table tb_part_parent(
  col  number primary key,
  col2 number
)
partition by range (col2) (
  partition part_1 values less than (100),
  partition part_2 values less than (300),
  partition part_3 values less than (500)
)

create table tb_part_child(
  col  number not null,
  col2 number,
  constraint fk_parent_1 foreign key(col) references tb_part_parent(col)
)partition by reference (fk_parent_1)


The query:

select t.table_name
  from user_constraints t
 where t.constraint_name in ( select w.r_constraint_name
                                from user_constraints w
                                join user_part_tables q
                                  on (q.table_name = w.table_name and
                                      q.ref_ptn_constraint_name = w.constraint_name)
                              )


Result:

TABLE_NAME
-----------------
TB_PART_PARENT