You can quickly identify hosts missing a sensor by going to Assets > Hosts. You'll see a count for "Hosts missing Sensor". Click this value to update the Hosts list to only show the hosts missing a sensor.
We use Information Gathered QID 48030 "Qualys Container Security Sensor Detected" to determine if a sensor is installed on a host. QID 48030 can be detected by a vulnerability scan using a Scanner Appliance or Cloud Agent. You can view vulnerability details for the host in the AssetView app. If QID 48030 has not been reported on the host then we consider the sensor missing.
Run a new vulnerability scan on the host or wait for the next cloud agent scan to see if QID 48030 is detected. If detected, the host will no longer be counted as missing the sensor.
We also suggest you look at the results section of Information Gathered QID 370440 "Docker Running Container Enumerated" to see whether the sensor is listed in the results.