How can I express the concept "There's nothing of which I'm absolutely sure" in Chinese?
1) (对)任何事情我都没有绝对的把握.


There is nothing wrong in this sentence, but it focuses on personal belief, a little bit inclining to the speaker's subjectiveness.

If we want to state something that describes a general belief, which focuses more on objectiveness, then we can say:


  2) (对)任何事情 我们 都没有绝对的把握.
  
  3) (对)什么事 我们 都 不可能有 绝对的把握.


Sentence 2 generalizes the idea expressed in sentence 1 by replacing 我 with 我们. 我们 covers not only the speaker, but also the readers and listeners.

Sentence 3 makes it even stronger, which emphasizes on the impossibility of having, while in sentence 2 没有 just describes the fact of not having.

Note: 任何事情 in sentence 2 is same as 什么事  in setence 3, no differences at all, they are interchangable.