There's no capability to get back from a Source monitor item to the actual projectItem, in PPro CC 2015.
However, you wouldn't be the first to request such functionality, and (ahem) I can neither confirm nor deny that it may be added in the near future.
Thanks, bbb. I can (ahem) confirm that that would be amazing. The scripting ecosystem that's built up around After Effects over the last few years is incredible. If Premiere got to that same level of scriptability, it would be a killer, and, as far as I know, unique, feature among mainstream NLEs. (And yes, I've filed a feature request).
I need also to get IN and OUT points from source monitor...
The idea is to send footage to fter Effects and replace them in a comp...
You can add my vote to this feature request.
Is there any progress on this request? Would love to be able to the project item based on what's loaded in the Source or Program Panel. Anything under the hood of app.enableQE?
I have no publicly available news on that front.
Partial workaround = get the path from the Source monitor, then use app.project.findItemsMatchingMediaPath() to find related projectItems.
Actually that might very well work.
While we're at it, any way to load an item into the source monitor by bin items (as opposed to via media path) -- Actually I'll post as a separate question... Is it possible to load a bin item in the Source or Program Panel?