I think GetInvocationList() may get the results you're looking for?
If we are dealing with an "event" rather than a raw "delegate", then
GetInvocationList cannot be called from outside the owner of the event. The
external client can only use += and -= on the event (that's basically what
the event keyword does).
So, unless there is some tricky thing using reflection that I don't know
about, I think the answer here is "no".