bazel build host/frontend/vnc_server/:vnc_server
The vnc server receives frame updates from the hwcomposer through the shared memory, for which it needs to connect to the ivserver. To send input to the instance it temporarily connects to monkey, which is set up to run on the instance as a service and listens on port 6445, so you need to forward that port to a local socket.
adb shell ps -e | grep monkey
adb forward localfilesystem:/tmp/android-cuttlefish-1-input tcp:6445
bazel-bin/host/vnc_server/vnc_server --port=6444 --input_socket=/tmp/android-cuttlefish-1-input
The VNC server will then be listening for connections on port 6444 on the host.