To resolve this QoS mapping issue on AOS-CX, you must understand the hierarchy of Trust Levels and how they interact with Link Aggregation Groups (LAGs).

Trust Hierarchy: AOS-CX switches use a " top-down " approach for QoS.

Global Trust: Setting qos trust dscp globally means that, by default, every port on the switch will look at the Layer 3 DSCP markings to determine queue priority.

Interface Override: You can override the global setting on a per-interface basis. If a specific device or service (like the video streaming service in this prompt) relies solely on Layer 2 CoS (802.1p) markings rather than DSCP, the switch will ignore those CoS markings under the global DSCP policy and place the traffic in a default (best-effort) queue.

LAG Configuration Logic: In the AOS-CX architecture, a LAG is a logical interface (interface lag 20).

Configuration parameters for the bundle (such as VLANs, ACLs, and QoS trust) should be applied to the logical LAG interface, not the individual physical member ports (1/1/20 and 2/1/20).

Once applied to the LAG, the settings are automatically inherited by all physical members.

Analyzing the Options:

Option D (Correct): By entering the interface lag 20 context and applying qos trust cos, you are instructing the switch to ignore the global DSCP setting for this specific bundle and instead trust the Layer 2 priority bits. This allows the video service to once again map correctly to the intended priority queues.

Option A: This is unnecessarily complex. Setting the physical member ports to qos trust none and then the LAG to cos is redundant because the LAG configuration overrides the physical port settings in this context.

Option B: qos trust dscp, cos is not a valid AOS-CX command. Unlike the older AOS-S (ProCurve) software which allowed a combined dscp-cos trust, AOS-CX requires you to choose a single trust type (DSCP, CoS, or None) per interface.

Option C: This applies the configuration to the physical ports only. In an AOS-CX VSF/LAG environment, this is considered a configuration error or " best practice " violation, as the logical LAG interface should hold the configuration.