If you search for 'octane' in the list of universal OBD parameters attached, you won't find any matches. That doesn't mean that a modern ECU doesn't have some sort of way to respond to knock. There is no universal parameter to log knock learning; you'd have to read RAM addresses directly, with an application-specific tool.
As I mentioned above, there are more sophisticated ways knock control can be done. It's not just interpolating between maps intended for high and low octane, although that's what say Mitsubishi has typically done. Up until now at least, Subaru hasn't been doing it in exactly that way. Here is a very good writeup on the Subaru knock-control system, at least up through the current WRX/STi
http://www.romraider.com/forum/viewt...hp?f=25&t=1840