Finally i figured out, that only the PostgreSQL table_types "VIEW" and "BASE TABLE" are listed in the Qlik data manager. Foreign Data Wrappers (FDW) are in PostgreSQL internally signed as "FOREIGN". Thats seem to be the reason why they are not listed.
But if you have set the correct access rights, then u can use them, although you dont see them: just try to make a simple SQL SELECT * FROM {my_fwd_table} and u will get all the data out of your FDW.