Seems like we are splitting hairs. Isn't "investigators could not determine what information about the site’s security the gunman gleaned" the same thing as "they cannot determine what he looked at"?Of course they have the logs and of course they know how to read them.
Here's what the article said, "Because there was no memory card in the drone, investigators could not determine what information about the site’s security the gunman gleaned from it, officials said."
The author of the article is not speaking for the Secret Service. The only thing to be concluded from that statement is that there was no memory card in the drone. The article does not say that "they cannot determine what he looked at."
In any event, no memory card was found in the drone when it was recovered from his vehicle. Whether there was one present during his flights is unknown.