Even if you explained exactly what it was, and gave them directions for reading it including all the coding conventions etc., they still couldn’t do it. Too many levels of dependent technology (i.e. you don’t have lasers. Tell them how to build a laser diode, but that requires a fabrication plant. Tell them how to build the fabrication plant and they can’t because the plant requires automation that doesn’t exist. etc.)
Look at the airplane: people understood the basics of flight for several hundred years before the Wright Brothers came along. But no one could build a powered aircraft because steam engines were too heavy and gasoline did not yet exist. And once gasoline engines came along, it still took a few decades before engines were light enough to give the power-to-weight ratio needed for flight. Once that threshold was reached, aviation exploded. If the Wright Brothers had never existed, we still would have had flying powered aircraft within a couple of years of their flight.
Nobady has mentioned the most astonishing thing they would find other than plastic. A CD will act as a wonderfull diffraction grating. From the diffraction, physicists would almost certainly figure out the nature of the grooves though I doubt if they could resolve any information.
Actually, I am not certain, but they may have had diffraction gratings back then. In which case, any physicist would be totally amazed at the precision and size of the grooves, since back then they would have been made mechanically.
I suspect that scientists would surprise you with their ability to figure things out. If they knew data was there, it could be read without a lazer or a microscope. Monochromatic light was available. High intensities would be difficult to attain, but not unattainable. From there a patern could be read.
Unfortunately, interpereting the pattern would be nearlyy impossible as fourier transforms had not been described yet.
As far as I can tell, there is no need to understand quantum mechanics, only mechanics of a light wave.
I’m not saying that they would figure all this out, but there certainly were those scientists that could have.