create table data (id integer, params jsonb);

insert into data values (1, '[
    {
        "prop": "a",
        "answer": "123"
    },
    {
        "prop": "b",
        "answer": "456"
    }
]');

select id, 
       tmp.parameters->>'prop' AS property, 
       tmp.parameters->>'answer' AS answer
from data
left join LATERAL jsonb_array_elements(data.params) 
          WITH ORDINALITY AS tmp (parameters, row_number) ON true
where tmp.parameters->>'prop' = 'a';