As no-one else who knows has yet replied, I'd guess you will find it behind a headlight inside a wheelarch liner if you cant see it under the bonnet, just a guess.... see where the filler neck leads you...?
drivers side, right behind the head light. will have a black cap (if its not missing). if you want to get to the actual bottle it is behind the wheel arch liner and right behind the radiator.
VV this should of been asking in the cinq/sei tech section mate. VV