My devices - list
How can I visualize a list of my devices that are using my apple ID? Do I have a way to identify them all?
iPad Air
The only way to know which devices and/or computer's iTunes are logged into your account for the stores is directly on them, there isn't a list.
If they are associated to your account (e.g. iTunes Match or automatic downloads have been used on them, or past purchases have been redownload on them) then they might show in the 'manage devices' section of your account : Manage your associated devices in iTunes - Apple Support
And/or if your account is being used for the cloud and Find My iPad/iPhone is enabled then they should show on http://www.icloud.com on a computer, and the Find My iPhone app on an iOS device (they might be using a different account for the stores).