There used to be a way to list all the dashboards that you have access to (your own, plus any you are an editor of). Can't find it now, and am wondering where to go looking.
You automatically have access to your own dashboard, and can get there from https://twitch.tv/dashboard which will redirect to https://twitch.tv/YOURNAME/dashboard/live; substituting someone else's channel name will give you a cut-down editor-only dashboard for that channel (unless you don't have access, of course). So one valid answer would be a way to find all channels you've been given editor access to.
Best Answer
Found it. In the current Twitch dashboard (as of 2019-03-21), you can find the channels you're an editor of here: https://www.twitch.tv/rosuav/dashboard/settings/managed-channels