Truncate is a DDL command and I don't think you can fire DDL command from Pega (Although Pega internally fires it). I would recommend you can create a Connect-SQL and use the Delete operation and commit the changes in any activity / Utility as per your requirement.
Any way you have to pass the list of table to truncate the data. May i suggest following high level pointers.
1. You can refer the table name using a Pega class name if you have created the respective Data-Admin-DB-Table entry for the same.
2. You can refer PageName.pxObjclass to identify the table.
3. In a agent activity, do a page-new with the proper class name and on that step page call the Connect-SQL rule which is stored in a common class up the hierarchy like organisation level or framework layer.