The suggested answer is B.
To troubleshoot call failures on an H.323 gateway and to see the signaling for media and call setup, the administrator should use the command 'debug H.225 asn1'. H.225 handles the control signaling for call establishment, call termination, and call control among H.323 entities in the network. The H.225 protocol includes H.225.0 call signaling and the RAS (Registration, Admission, and Status) protocol, necessary for seeing the required signaling information.