I hope you are talking about Jira Filter Subscription, here is cron expression that will satisfy your need.
0 0 0 1,15 * ?
This expression run your subscription on 00:00 hours every 1st and 15th of every month.
Hopefully this helps.
If you want to learn more about cron expressions here is link - https://confluence.atlassian.com/jiracorecloud/constructing-cron-expressions-for-a-filter-subscription-765593786.html
Unfortunately, cron expressions do not natively support the "every two weeks" time period.
There are workarounds that might work for certain scenarios, but I'm afraid none of them would work for filter subscriptions.
However, there are very convenient and free Cron Expression Generators online that might help you get the alternative that best suits your needs:
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