Quēn in? or Quēnin in? = How so?
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 132.
yc queni monavatilli = what is to be ordered about (Tlaxcala, 1547)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 22, 120–121.
namechnanquiliz quenin mochivaz = I will answer how it is to be done
(Tlaxcala, 1547)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 22, 118–119.
quimilhuique quenin tla oc ceppa = they said to them: What is this? Say again
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 2, 45–46.
yn quenin = a statement, not a question
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.
quenin = the longer form of quen (and to have a longer form is the case with many interrogatives), giving a slightly stronger sense: "how is it possible that...?" or "how is it the case that...?"
Michel Launey, An Introduction to Classical Nahuatl, translated and adapted by Christopher MacKay (Cambridge: Cambridge University Press, 2011), 132.