The missing parameter shown as the highlighted question mark in the exhibit for configuring inter-VLAN routing is the VLAN ID after the command encapsulation dot1q. This VLAN ID is a numerical identifier unique to each VLAN in the network and is essential for properly tagging VLAN traffic when encapsulation (using 802.1Q) is configured on a router subinterface. The command typically looks like this:

encapsulation dot1q <VLAN_ID>

For example, if the VLAN ID is 7, the full command would be:

encapsulation dot1q 7

This encapsulation type specifies how traffic is tagged for the VLAN, and the VLAN ID identifies the specific VLAN for the subinterface. This parameter is critical for inter-VLAN routing so that the router can correctly route traffic between VLANs. In summary, the missing parameter is the VLAN number (VLAN ID) that follows the encapsulation type in the configuration command for inter- VLAN routing.