Grab any list of the top domains on the Internet. My go-to has been the "Moz 500" --- I don't know what it is, or whether it's any good, but it's easy to get. Then write the trivial shell loop to `dig ds $domain`, and count how many of the top domains are signed. Some patterns will emerge: government sites, unsurprisingly, have subscribed themselves to the de jure government PKI that DNSSEC is, and commercial sites overwhelmingly do not.

It's very easy to just check this for yourself. There are increasing numbers of domains signed every year, because registrars and product companies have baked DNSSEC in as a feature. But the vast majority of zones don't matter: nobody ever looks anything up in them. The figure of merit is how many important zones are signed.