Witness
noun
An evidence person is a witness, because witnesses are people who provide evidence (you know, with their mouths or something).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
証人の場合
in the case of a witness
証人の出頭
the appearance of a witness
証人の証言
a witness's testimony
成人の証人
an adult witness
他の証人
another witness
エホバの証人
Jehovah's Witnesses
証人に立つ
to stand as witness, to bear testimony
証人にする
to make into a witness
証人になる
to become a witness
証人はいません。
There are no witnesses.
私も証人の一人です。
I am also one of the witnesses.
彼はエホバの証人です。
He is a Jehovah's Witness.