I've spent a good portion of the morning trying to get more information about trigger tokens and there really isn't much, or at least not much I can find. I checked the Product Docs and all I found was a list without much explanation of what they returned or where they worked or the rules.
I played around and found a couple of trigger token values by running tests but then dumped a bunch into one SC and it failed because some of the tokens were invalid. This concerned me. I'd rather see an "undefined" for an invalid token than the entire CDV fail.
I don't know if you saw this, but there's more info on the trigger tokens and where they can be used here: Tokens for Interesting Moments - Marketo Docs - Product Docs
The grid in the document has a horizontal scroll bar that will allow you to see the full chart of the tokens and which triggers they work with.