You may locate this information in the SentDate column of the BBNCEmailRecipients table. Generally, NetCommunity (BBNC) related information would be found in the tables prefixed BBNC in The Raiser's Edge (RE) database. If you would like to view more details about the RE tables and how they relate to each other, the link below shows how to view the database schema.

How to find a database reference definition or schema (includes video demo)