Why do you know such a difficult word but not an easy one like this?
"何でそんな難しい単語知っててこんな簡単な単語知らないの？"
- Why do you know such a difficult word but not an easy one like this?
- How do you know a difficult word like that but not an easy one like this?
- How do you know a hard word like XXX but not an easy one like XXX?
XXX -> 単語を入れる
How do you know such a difficult word like that, but don't know a simple word like this?
この場合、次のような言い方ができますよ。
ーHow do you know such a difficult word like that, but don't know a simple word like this?
「そんな難しい単語を知っていて、どしてこんな簡単な単語がわからないの？」
「簡単な単語」は a simple word とも言えます。
ご参考まで！
アメリカ合衆国 
カナダ 
