The missing parameter shown as the highlighted question mark in the exhibit for configuring inter-VLAN routing on a network is the type of encapsulation that is used. This parameter is essential because inter-VLAN routing requires trunking encapsulation, typically IEEE 802.1Q, to identify how VLAN tags are used in the network traffic passing through the router or Layer 3 switch subinterfaces. The encapsulation ensures that traffic is properly tagged for each VLAN for routing purposes. Without specifying the encapsulation type, the device cannot correctly route traffic between VLANs. Other parameters like subinterface identification or VLAN number are also important but are not the missing piece indicated by the question mark in this context. The encapsulation type is the critical missing parameter that enables inter-VLAN routing configuration to work correctly. Thus, the missing parameter is: It identifies the type of encapsulation that is used.