How to say that you need to do something?


What's the best way to say that someone needs to do something, as in "5
English slangs you need to know"? I found some ways

> 知る必要があるの5つ英語のスラング。  
> 知らないといけないの5つ英語のスラング。  
> 知るべきの５つ英語のスラング。

Which is more correct or in what context should each be used? Is there a
better way to say this?




First of all, one の is necessary between 五つ and 英語、and the first の is not
necessary and the second の can be omitted such as 知る必要がある5つの英語スラング.

知る必要がある is "you need to know".

知らないといけない(知らなければならない) is "you must know".

知るべき is "you should know".

