Just tune into a station. If it has HD, itll switch or you'll see it on the screen. For example, here in LA, 102.7 has 1/2, meaning it has 2 HD Channels on that frequency you can switch to. Posted via the PriusChat mobile app.
I found the HD on/off button. Press audio. Then press source. Then press options. And you will see the HD radio on/off.