How can I populate my Contact List in icloud.com with the contents of an backup of two weeks ago which is still in my icloud?

The only way to use any of the information from a backup is to restore the iOS device from that backup. Individual content is not available in the iCloud backup. You have to restore the device all or none. You cannot put backup into iCloud Contacts. You can only do that from the iOS device, or if you have the content in another format you can upload to iCloud using the computer, but that cannot be obtained from the backup.