<p>A multi-layer network can simulate real networks more objectively than a single-layer network due to its inherent hierarchical structure. Inspired by this observation, this paper investigates the consensus control problems of two-layer networks with directed switching topologies. First, we design the unknown input observer based on relative output states (ROS). With the aid of this observer, the event-triggering control protocol based on ROS is proposed. It is shown that under the proposed consensus control protocol and given assumptions, if the average dwell time is larger than a given positive threshold, consensus can indeed be reached. Moreover, two comparisons with the results in the existing works based on the lead-acid battery model and the satellite model are finally displayed to illustrate excellent consensus performance under the control protocol proposed in this paper.</p>