Primary & foreign keys and the tables & columns they reference.
Referenced primary keys
Simple query that lists all primary keys and the tables & columns they use. Adjust the where clause to your needs.
Hierarchy of primary & foreign keys
A more complex query:
This will travel the hierarchy of foreign keys for a given table and column and return columns from child and grandchild, and all descendant tables.
It uses sub-queries to add r_table_name and r_column_name to user_constraints, and then uses them to connect rows.
Adjust the where clause to your needs.
Either run these as sys/system, or give the user these 2 privileges:
You can find the original queries here; I did change them quite a bit to make them more legible and to use the dba_% views: