Why can't i see what is stored in my iCloud for any of my devices ?

To see the contents of actual data in iCloud, log into iCloud.com as Eric Root advised and use the various apps there to see what is stored in iCloud.

For a more general overview, click on this link to read how to 'Manage your iCloud storage' --> https://support.apple.com/HT204247 - including seeing how much storage you have and how to delete items stored in iCloud such as backups, photos, files, mail, messages and voice memos.

Have you logged into iCloud.com using a browser? You can't see backups or messages stored in iCloud.