Writing Email script token to pull Expire Date for Specific Assets only (SFDC assets)

I'm trying to create some renewal outreach for subscribers of a specific service.  Our services are managed by use of SFDC "asset" objects, which we have synced with Marketo.  I'm trying to create a token for subscription end date which is a field on the SFDC asset, but I need to ensure it's pulling the date from the correct SFDC asset, because it's possible for a person to have several assets with different expire dates.  Any thoughts on how to construct this using the Email Script option in the Token area? I've found the custom Asset object and its fields in the Email Script object, but am unsure about the syntax needed in the script.

Thanks for any tips and advice!