Is There an adb/shell command to list the items on the android's notification bar?

You can use

adb shell dumpsys notification

It shows detailed information about currently displayed notifications.

On Android >= 6 for get notification extras use this command

adb shell dumpsys notification --noredact

the full notifications text you can see at the extras section:

      extras={
          android.title=String (Bring The Rain)
          android.reduced.images=Boolean (true)
          android.subText=null
          android.template=String (android.app.Notification$MediaStyle)
          toSingleLine=Boolean (false)
          android.text=String (Upon A Burning Body)
          android.appInfo=ApplicationInfo (ApplicationInfo{c8165e6 org.telegram.messenger})
          android.showWhen=Boolean (false)
          android.largeIcon=Icon (Icon(typ=BITMAP size=100x100))
          android.mediaSession=Token (android.media.session.MediaSession$Token@608a746)
          gameDndOn=Boolean (false)
          android.compactActions=int[] (3)
            [0] 0
            [1] 1
            [2] 2
      }

adb shell dumpsys notification | grep ticker | cut -d= -f2

shows me a little description of the texts of the screen. tickerText appears to be the name of the property which contains the text of the notifications