Fetch the DB Object Backed by an External Database

SELECT
    OBJECT_SCHEMA_NAME(d.referencing_id) AS referencing_schema,
    OBJECT_NAME(d.referencing_id)        AS referencing_object,
    o.type_desc                          AS referencing_type,
    d.referenced_database_name,
    d.referenced_schema_name,
    d.referenced_entity_name
FROM sys.sql_expression_dependencies d
JOIN sys.objects o 
    ON o.object_id = d.referencing_id
WHERE o.type IN ('P','V') -- P = SQL Stored Procedure, V = View
  AND d.referenced_database_name IS NOT NULL
  AND d.referenced_database_name <> DB_NAME()
ORDER BY d.referenced_database_name, referencing_type, referencing_schema, referencing_object;

Gives database object which uses external database.