When ClamWin reports a ClamAV database identifier like Win.Trojan.Agent-1698031, how can we find information about that malware?

Someone entered it into the DB, so someone must have known and recorded when it was found, what it does, and what OS or software versions are known to be vulnerable to it.

As far as I am concerned, ClamAV doesn't post information of malware anywhere on their site. You could always look up if another AV says about it. It would be the same file, same signature, but under a different name.