High Kens is "a highly formal and archaic version" of Kens, the Kencyr language. It does not appear to be known by all Kencyr; the only people who appear to understand and speak it are all Highborn.
Ishtier uses it to test Jame's origins in God Stalk, and she uses it again to curse him when she discovers what he did with Bane's soul.
↑To Ride a Rathorn, "Glossary" — "High Kens: a highly formal and archaic version of the Kencyr language"
↑God Stalk, Book I: Tatters of Dusk, "Chapter 3: Into the Labyrinth" — " 'That is but half a name. Tell me the rest.' 'With respect, my lord, it does not concern you.' She did not realize until she saw his slight smile deepen that he had asked and she replied in High Kens."
↑God Stalk, Book III: Shroud of Days, "Chapter 14: Untempling of the Gods" — " 'You betrayed him first, by agreeing to carry his soul and then by using it in such a damnable manner,' Jame cried, unconsciously shifting into High Kens as shock changed to fury."
↑Seeker's Mask, "Interim VI: Gothregor" — " 'My lord,' said Adiraina stiffly, in High Kens. 'This invasion is inexcusable. Withdraw at once.' "
↑To Ride a Rathorn, "Chapter XVII: Into the Wilds", VI — " 'Soft,' said a voice behind her, odd and husky as if it hadn't spoken in a long time, and it spoke in High Kens."
↑Bound in Blood — "mixed with bawdy jibes from the men about the supposed pleasures of her wedding night. Hopefully no one understood the answers that she snarled back at them in High Kens, a language rich in courtly invective."
↑To Ride a Rathorn, "Chapter VII: In the Bear's Den", I — "the Jaran, a shouted phrase in High Kens: 'The shadows are burning!';"
↑ 8.08.1The Gates of Tagmeth, "Chapter III: Northward Bound", VIII — " 'So we have called every leader of our house since the Fall, as a sort of joke. It's High Kens for "servant," or, more loosely, "one who has no time to read." ' "