What are the best words that approximate the meaning of "cynical" closest? The traditional "憤世嫉俗" sounds not quite to-the-point; "憤世嫉俗" can be attached a positive meaning that describes the character of an upright man.
KEY defines it as:
cynic (esp. as Greek philosophical school)
and 汉语大词典 defines it as:
原指古 希腊 犬儒学派的哲学家。他们提出绝对的个人精神自由, 轻视一切社会虚套、习俗和文化规范, 过着禁欲的简陋生活, 被当时人讥为穷犬, 故称。后亦泛指具有这些特点的人。
Here’s an example of usage by 鲁迅 from Miscellaneous Thoughts
蜜蜂的刺, 一用即丧失了它自己的生命；犬儒的刺, 一用则苟延了他自己的生命。
Which translates to something roughly like:
The sting of a bee, once used terminates his life; the sting of a cynic, on the other hand, is able to prolong his existence.
Eileen J. Cheng's translation:
Once a bee uses its sting, it loses its life immediately. Once a cynic uses his sting, he drags out his life momentarily.
If it is good enough for Mr. Lu Xun then it should be good enough for anyone.
acrid; acrimonious; tart; sarcastic; mordant
尖= sharp (tongue); 酸= sour (tone). It is how 'cynical' feels like. A '尖酸' person is a 'cynical' person
sharp and unkind (words)
It can also be used as an adjective to describe a personality
玩世不恭 could be the one that comes to my mind. It has a similar meaning as 愤世嫉俗, which is cynicism or be cynical.
A lot of the Chinese words used to translate the word "cynical" don't seem to convey the idea of "not trusting a given (or accepted) answer" or "questioning". "愤世嫉俗", for example, really has to do with feeling outraged at social injustice (and lack of enlightenment). "玩世不恭" describes the type of person/attitude where one takes nothing seriously (esp. in regard to social, political matters). "犬儒学派" goes to the ancient Greek root of the word "cynic" ("dog" or "dog-like" - which describes someone like Diogenes)--which is not wrong, but how many English speakers associate the word "cynic" with "dog"? "非信非疑" isn't quite right either, because it simply states "neither believe nor disbelieve"-not exactly "actively questioning".
The closest I have come across is "持怀疑态度". Although this is not a catchy 成语 (proverb), it expresses the idea of "actively not believing". "怀疑", by the way, means "suspecting" by itself, but "怀疑态度" is the "attitude of not believing/accepting without questioning".