If you want to check your devices for TV Anywhere then you can sign into your account, on the right hand side you will see My profile, under here will be Device Settings. Once you click onto that you will see the registered devices.
For Sky apps, the same as for TV Anywhere, sign into your account and under My Profile this time select Sky Movies & Sky Sports.
If you want to change them you have one available device change each month for both sections. You can remove them from the list and to register the device start streaming a channel on either TV Anywhere or through a Sky app (depending on which you want), this will then prompt you for registration and then it will start to work.