PostgreSQL: Check the structure of foreign tables
How can I check if the structure of a foreign table was changed in the
  source database in order to know when to re import it. Foreign table
  was imported by foreign-data wrapper postgres_fdw.


As here and here if you’ve imported your schema, then you can query the foreign tables as if they were normal, local tables.

For further your ref postgres_fdw and IMPORT FOREIGN SCHEMA