To turn on Alexa Captioning, go to the device settings on your Echo Show or Echo Spot, select accessibility settings and tap on Alexa Captioning.
You can then customise the captions that appear on your screen depending on your preferences.
Amazon is also introducing Tap to Alexa - also for devices with a screen. Available in the US only for now, you can ask Alexa for things like weather, timers, and traffic by touching the screen. It's designed for people who aren't able to ask Alexa by voice.