Case data is stored in pc_work table. Please refer the following link for more information: https://community.pega.com/sites/default/files/help_v81/procomhelpmain.htm#engine/database/tables/eng-db-case-tables-ref.htm

pc_data_uniqueid, pc_work, pc_history_work, pc_assign_worklist, pr_sys_queue_ftsindexer(incase indexing is enabled), cache tables

Case data is stored in the table your class group is mapped to. Open the class that you have identified as the class group and click Test Connectivity. You should be able to see the table name in the result. Assignments are stored in pc_assign_worklist or pc_assign_workbasket, attachments are stored in pc_data_workattach and pc_link_attachment.