The sentence you wrote is mostly correct! Here's the sentence:
The elephant has a long trunk to reach for juicy fruit from tall trees.
However, you can make it sound smoother by removing the word 'for' after 'reach'. The corrected sentence should be:
The elephant has a long trunk to reach juicy fruit from tall trees.
Explanation: When you use 'reach' followed by what you want to get, you don't need 'for'. For example, you say 'reach the shelf,' not 'reach for the shelf.' But if you say 'reach for something' by itself, that means you are trying to grab it in general. Since your sentence directly says what the elephant is reaching, just say 'to reach juicy fruit.'