Postgres 12

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WITH mytable AS (
    SELECT '{"territory_custom":[{"name_directory":"ЯПОНИЯ","id_ref_directory":38},{"name_directory":"ЯПОН","id_ref_directory":39},{"name_directory":"ЯП","id_ref_directory":40}]}'::jsonb AS mydata
)
SELECT * FROM mytable

mydata

{"territory_custom": [{"name_directory": "ЯПОНИЯ", "id_ref_directory": 38}, {"name_directory": "ЯПОН", "id_ref_directory": 39}, {"name_directory": "ЯП", "id_ref_directory": 40}]}

WITH mytable AS (
    SELECT '{"territory_custom":[{"name_directory":"ЯПОНИЯ","id_ref_directory":38},{"name_directory":"ЯПОН","id_ref_directory":39},{"name_directory":"ЯП","id_ref_directory":40}]}'::jsonb AS mydata
)
SELECT
    jsonb_path_query_array(mydata, '$.territory_custom.id_ref_directory') elems
FROM mytable
    
elems

[38, 39, 40]

WITH mytable AS (
    SELECT '{"territory_custom":[{"name_directory":"ЯПОНИЯ","id_ref_directory":38},{"name_directory":"ЯПОН","id_ref_directory":39},{"name_directory":"ЯП","id_ref_directory":40}]}'::jsonb AS mydata
)
SELECT
    array_agg(elems::int)
FROM mytable,
    jsonb_path_query(mydata, '$.territory_custom.id_ref_directory') elems

array_agg

{38,39,40}