Dokusan (Chinese, ducan; Korean, tokch'am) is a private consultation between a Zen master and a student.
In the Rinzai school, a Zen sect of Japanese Buddhism, dokusan (also called sanzen) is used to gauge a student's development. The master questions the student to test his understanding of a koan, the critical phrase of which he has meditated on as part of his training. The student passes by giving correct (viz. what his master's lineage has considered correct) answers. Like for most tests, these answers are supposed to be kept secret, but, like for most tests, there are cheat sheets. However, the idea that dokusan can be cheated seems to reflect a lack of belief or understanding of Zen; Zen masters are said to be able to tell a rote answer from a truly insightful one.
References:
Dokusan. (2013). In R. E. J. Buswell, & D. S. J. Lopez (Eds.), The Princeton Dictionary of Buddhism. Princeton, NJ: Princeton University Press.
Schlütter, Morten. "Kōan." Encyclopedia of Buddhism, edited by
Robert E. Buswell, Jr., vol. 1, Macmillan Reference USA, 2004, pp. 426-429. Gale Virtual Reference Library. Accessed
20 Nov. 2017.