Go to the TTN main page, scroll down to the map with gateways and zoom in on the location of the gateway. Once you click on the gateway it will show a contact option.
To find the location of the gateway as registered with TTN you can use the https://account.thethingsnetwork.org/api/v2/gateways/eui-0000024B080E0D5C . It lists the coordinates. (Also lists the user which can be appended to http://www.thethingsnetwork.org/u/ to find the user, the user page also contains a contact option)