Purchased products via a website
How do I find the location of the purchased product/subscription I made through a website
Your question is not very clear.
Use the app that the subscription is supporting. For example, if this is a subscription that offers additional features for app 123, open app 123 to view and use those features.
If you subscribed through a website, this won't be an Apple subscription and any support will have to come from the app developer/vendor directly. Apple won't have a record of it.