If you export a QuickTime ProRes from Premiere with timeline markers, then import it into After Effects, and drag it into a Comp, Ae automatically shows the timeline markers as layer markers.
I need a way to programattically grab this metadata from an arbitrary QT video file. But I've Googled high and low and found nothing. I've tried examining the QuickTime file with all kinds of tools and haven't found where these markers are stored. They've got to be in there somewhere.
If you're trying to access the data via Ae scripting, you should just be able to step through the markers. If you're trying to access the data outside of Ae, maybe the XMP SDK will help you: https://www.adobe.com/devnet/xmp.html