Don’t we all?
The speaker thinks that everyone shares the predicate of what the previous speaker says. 
Even though the speaker says "all", it can be just two people (Speaker 1 and 2) present.
E.g. 
Speaker 1: I hate science.
Speaker 2: Don’t we all (hate science)?
 (this speaker thinks that everyone shares the predicate "hating science")

Example:
▪ I need more money.
▪ Don’t we all? (Everyone needs more money, right? We all need more money, don’t you think?)
▪ I wish I had more free time.
▪ Don’t we all  (We all want more time, right? Everyone wants more time, don’t you think?)

轉載自：
https://hinative.com/zh-TW/questions/4618524