requête :

SELECT routines.routine_name, parameters.data_type, parameters.ordinal_position
FROM information_schema.routines
    LEFT JOIN information_schema.parameters ON routines.specific_name=parameters.specific_name
WHERE routines.specific_schema= 'nom_du_schema'
ORDER BY routines.routine_name, parameters.ordinal_position;

example :
SELECT routines.routine_name, parameters.data_type, parameters.ordinal_position FROM information_schema.routines LEFT JOIN information_schema.parameters ON routines.specific_name=parameters.specific_name WHERE routines.specific_schema= 'public' ORDER BY routines.routine_name, parameters.ordinal_position;