By his wisdom, his behavior, everything. Truly enlightened
people no longer have any Greed, Hatred or Ignorance. An
enlightened person is really quite different from usual sentient
beings like us.
A truly enlightened person also no longer has the Three Minds (any
attachments to Past, Present, Future) and "no ego form, no human
form, no sentient being form, and no age form" as stated in the
Diamond sutra.
An Arhant has also removed the 10 fetters: "self-illusion,
skepticism, attachment to rules and rituals, sensual lust, ill-will
/ fine material existence, immaterial existence, conceit,
restlessness, ignorance"
As for the 'Zen Master' koans, there is one example in the
internet: http://www.kwanumzen.com/dssn/
It is an interesting read, it is about the story of how Zen Master
Seung Sahn got the transmission and recognised as enlightened by
his master. He had to pass through many tests.
