You must have already added an after event because this shows up in UD05 when starting fresh. Go in your actual list of events and do a search for custom events. If it still doesn’t show up, close everything and log back in again.
… I just wanted to chime in that the event name doesn’t need to include “after” or “toolnew” or anything of that ilk.
Somebody could have created an event called “MyMagicSchoolBus”… and set the trigger to after onclick_toolNew.
You can only use those triggers once, and that’s why its not available for you.
So, yes, you can try to find the event that is running “after” the onclick_toolNew… but trying to find it by NAME could be a chore. It could be named ANYTHING.
Just jump into preview, turn on debugging, and watch what events fire when you click the new button.