How to say that you need to do something?

Question

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?

Answer 1

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".