Getting a Subrecord

The structure of the subrecord is also returned on the parent record, on the sublist line, if you set the expandSubResources query parameter to true  
GET operation, which is used to access a subrecord.
GET http://demo123.suitetalk.api.netsuite.com/services/rest/record/v1/customer/42/addressbook/24/addessbookaddress 
{
    "addressee": "Dwight Schutte",
    "city": "New York",
    "country": "US",
    "drop downstate": {
        "id": "NY",
        "refName": "New York",
        ...
    },
    "state": "NY",
    "zip": "10001",
    ...
}