Hi @TechOpsHub,
At this time, the best way to see all of the Subitem data is to first query the subitem Ids using the column_values field for an item.
Using this subitem Id, you can then find the subitem board Id, and then use that board Id to query information and make changes/mutations as you would with any other board.
Check out this thread for more info! Also feel free to dig around our community for other threads relating to subitems. There’s a ton!