To determine if a gateway is linked to an asset, go to the Gateways page and click on the gateway you want to check.
The Edit Gateway panels opens. Go to the Data Sources tab.

Click on the arrow behind a data source to see if the data source is used by an asset.
A new panel opens, listing all assets that were at one time linked to this gateway and have not been deleted yet.

If an End Time is set, and it’s before the current date (asset TRANS01 in the above screenshot), the asset is in essence not linked to the gateway anymore.
In other words, the End Time has to be a future time and date, or Not set, for the gateway to be effectively linked to the asset.
Hint!
Please make sure to check all listed data sources, since not all data sources have to be used by an asset.