Answer: In the plane of the paper itself, to be precise. The axis of the compass is vertical, and the magnetic field produced by the conductor is vertical as well. Because of this, it is not possible in this situation to have a dipping compass needle result (dips result only if the axis of the compass is horizontal). When the conductor through A is perpendicular to the plane of the paper, the deflection is greatest, and the field due to it is greatest when the conductor through A is parallel to the plane of the paper.