Ниже для BigQuery Standard SQL
#standardSQL
SELECT
( SELECT value.string_value
FROM UNNEST(event_params) param
WHERE key = 'item_name'
) AS item_name
FROM `project.dataset.table`
WHERE (
SELECT COUNT(1) FROM UNNEST(event_params) param
WHERE (key, value.string_value) = ('content_type', 'POI') OR key = 'item_name'
) = 2