In the Alexa app, tap Devices (at the bottom), Cameras, then the name of your Ring doorbell.
Now you are in the Alexa settings for your Ring doorbell camera. Tap Announcement Devices. Put a check mark on any device that you want the Ring doorbell to announce and show the video on. Echo devices that have a screen will show video and devices without a screen will get audio-only announcements.
One thing that I've noticed is that if you choose video announcements on several devices but your internet bandwidth is not great, you might not see the video on some of your devices. My internet speed is 30Mbps down/2Mbps up and if I choose 3 or more devices, the video usually won't come through.
Furthermore, if you have other devices that are also recording to the cloud (such as Wyze cams, Arlo cams, etc.) they are also using up your bandwidth at the same time that Ring is trying to send video to your Echo Show. That can affect your ability to view live video.