The Knight's Piece is a gamepiece which becomes an essential plot point in the third chapter of Betrayal at Krondor.
This article contains plot or ending spoilers.
The gamepiece can be found by using a Virtue Key at a well in Kenting Rush, although care must be taken not to leave it in a Sack or a unlocked Chest, where it could disappear and make it impossible to finish Chapter 3.
The Knight's Piece must be put in place on the chessboard at the Waterfall to unlock the secrets that will ultimately end the chapter.
In regular chess, the Knight is valued for its ability to bypass other gamepieces by "jumping" over them, an ironic point in light of the location where this one is used.