Images stored ON the iPad

It depends if you have a subscription (either the Lightroom Mobile one or a Photography Plan).

If you do have one, then images imported into the app or taken with the app's camera will upload to the cloud automatically. The full res image will remain locally within the app until the app's cache management replaces it with a thumbnail as other more full res recent files takes its place in the local cache. 

If you are using the free app, then they won't upload to the cloud.