I'm looking for an addon to mark a partymember, similar to the raid symbols, but only visible to me. Something like a giant arrow on the head of someone. Would be very practical in some boss encounters.
Basically it's not possible to get the on-screen position of any render object.
There's one exception: the nameplates.
It would be possible to attach a "marker" to a specific nameplate. Unfortunately the nameplates are visible in a very close range only.
So the answer is "no" ... at least not in a useful way. :/