Using the word 为止 (with a time phrase)
我沒知道存有椰子火鍋到他吃爲止。他吃椰子時(到)我沒知道此存有爲止。


There are a couple of things that needs to be addressed about the sentence - unfortunately, in its current state, it is not legible.


Chinese doesn't use the equivalent of English I never knew (我「沒」知道) - we usually say I didn't know (我「不」知道) or I've never heard of (我沒聽說過).
「存有」is an exceedingly specialised philosophical term; to literally say exists in everyday language, the term is「存在」. An example sentence might be


  Ｘ（這種東西）不存在。
  
  There's no such thing as X.

The use of「爲止」here is problematic, and others have addressed how to use this term correctly.


Using something natural like @xbh's example


  在他吃之前我都不知道還有椰子火鍋
  
  Before he ate coconut hot pot, I never knew it existed.


is recommended, but as an exercise in using「爲止」, you can construct a grammatically correct statement like


  我朋友剛剛吃了椰子火鍋。「到目前爲止」，我還不知道有這種東西。
  
  My friend just ate coconut hot pot. Up until now, I didn't know there was such a thing.