It's my understanding that the registrars are the ones with the burden here. They need to inform everyone of the data erasure and/or data updates on private information. Fun times when you have public information for anyone to gather on the internet. It could be that there are exemptions for these kind of services, I do not know, but would the exemption not also include the services that aggregate/collect historic information as well?
Disclaimer; I am not a lawyer. I am not well versed in GDPR. Anyone finding this interesting should go read up on GDPR.
It doesn't work that way. The "right to be forgotten" can be used to remove search results from Google, even if the original content stays up.
Under GDPR, Security trails (company or person that operates it) could be classified as a "Data controller" [2] and then would of course be liable to delete information gathered about a person upon request and when the data is deemed to be "inadequate, irrelevant or no longer relevant or excessive". So for example, John Doe wants to remove the historic information that he used to own porn.com which he doesn't anymore.
However, I do not think it's clear that you have to delete the data for the current owner of porn.com due to his or hers need for privacy as long as they have collect the information lawfully.
As an actual advice to the people at security trails I would recommend they put up clear instructions on how to request a data erasure from their database. Like "Email erasure@securitytrails.com to request removal of your personal information" and what information they need to delete it.
[1] https://en.wikipedia.org/wiki/Google_Spain_v_AEPD_and_Mario_...
[2] https://en.wikipedia.org/wiki/General_Data_Protection_Regula...
Edit: formatting