You can make a DCI with one of the following metrics: https://www.netxms.org/documentation/adminguide/service-monitoring.html#network-service-monitoring-using-dci
The DCI should be on a node that has agent running, e.g. on your NetXMS server node. But there's a way to overcome this - you can have this DCI on the node that you are monitoring and in properties of that DCI you can select another node in "Source node override" field.
