Use quest markers to indicate locations asked about

[PALU]

If it's easy to implement, using quest area rings to indicate approximately where villages, caves, and lakes asked about are would be rather helpful. If so, the areas would be automatically removed when the feature is seen by the character.
If you're told about a feature again the basic implementation would just keep the original indication, while an enhanced version would add something along the lines of "(you feel you have heard about this <feature> before.)".