-- Select <JSON_KEY1> value from <TABLE_NAME>.
SELECT <JSONOBJECT_COLUMN>::json->'<JSON_KEY1>' FROM <TABLE_NAME>;
-- Select <JSON_KEY1> JSONObject <JSON_KEY2> value from <TABLE_NAME>.
SELECT <JSONOBJECT_COLUMN>::json->'<JSON_KEY1>'->'<JSON_KEY2>' FROM <TABLE_NAME>;

-- Add "newKey" key and value "New key value" to <JSONOBJECT_COLUMN> in <TABLE_NAME>-table.
UPDATE <TABLE_NAME>
SET <JSONOBJECT_COLUMN> = COALESCE("<JSONOBJECT_COLUMN>", '{}')::jsonb || '{ "newKey" : "New key value" }';

-- Remove "removeThisKey" key and value from <TABLE_NAME> and <JSONOBJECT_COLUMN> columns
UPDATE <TABLE_NAME> SET <JSONOBJECT_COLUMN> = <JSONOBJECT_COLUMN>::jsonb - 'removeThisKey';