I've got nothing concrete either, but I think I have the two occassions where it is used in the game.

http://www.tlhingan.at/Misc/KCD_SOS_TAJ/mother_kill.mp4 <- one of the wrong choices, if you accuse your (poq's) mother (of killing your father), she'll offer her knife and tell you to use it. I don't think she's a warrior, so it's likely the SoS taj.

http://www.tlhingan.at/Misc/KCD_SOS_TAJ/mother_threaten.mp4 <- poq's mother threatens Vok (enemy of the house of SepIch), using a knife - it's not clear where it's from, but I assume it is her knife, not his.