A marketer has built an automation using Automation Studio to send data from adata extension...

If the fileis not showing up on the SFTP after a successful data extract, the missing activity is likely the File Transfer activity. This activity is responsible for moving the extracted .csv file to the appropriate directory on the SFTP server. Without this step, the file will not be transferred to the SFTP location.

References:

Salesforce Marketing Cloud Documentation on File Transfer Activity