The official IOTA FAQ mentions how Bitcoin needs roughly 6 blocks to verify a new transaction. What is the equivalent rough estimate for IOTA in order to verify a single new transaction? How big of a subtangle does a node need to verify a new transaction?
In IOTA, we don't have blocks.
Each transaction in the Tangle approves two previous transactions.
A confirmed transaction is one that is approved by the Coordinator.
You can read more about the Coordinator in the developer documentation.