The BOV should get manifold vacuum on the top port (it's actually a top-port even though it's on the side on yours). Any place where you're tapping in the boost gauge should be fine. Make sure the port you choose is behind the throttle-body so it picks up the vacuum condition when you close the throttle. That's what opens your BOV.
You don't want to hook your BOV, or boost gauge, to the reference-line coming from the turbo outlet to the wastegate. That should only be used for the wastegate (generally side port) and a boost controller if you're using one.