Dump pglogical Config to files
The table belongs to the extension pglogical, so pg_dump doesn't dump it.

Objects that belong to an extension don't get included in the dump, they are subsumed in the CREATE EXTENSION command from a database dump, because that object will be created by the CREATE EXTENSION command. If the object itself got dumped too, restoring the dump would cause an error, because the object already exists after CREATE EXTENSION.

You could use psql and do something like

\copy (SELECT * FROM pglogical.replication_set ORDER BY ...) TO 'some.file' (FORMAT 'csv')