The insertion point for East-West network introspection is the Guest VM vNIC. Network introspection is a service insertion feature that allows third-party network services to be integrated with NSX. Network introspection enables traffic redirection from the Guest VM vNIC to a service virtual machine (SVM) that runs the partner service. The SVM can then inspect, monitor, or modify the traffic before sending it back to the original destination1. The other options are incorrect because they are not the insertion points for East-West network introspection. The Tier-0 router is used for North-South routing and network services.
The partner SVM is the service virtual machine that runs the partner service, not the insertion point. The host physical NIC is not involved in network introspection.
Reference: Network Introspection Settings