Tell me what you like about him. I don't get what's so good about him.
What is that you like about him? I'm having trouble seeing his good qualities.
この場合、次のような言い方ができますよ。
ーTell me what you like about him. I don't get what's so good about him.
「彼のどこが好きか教えて。彼の何がそんなに良いのかわからない」
I don't get what's so good about ... で「…の何がそんなに良いのかわからない・理解できない」
ーWhat is that you like about him? I'm having trouble seeing his good qualities.
「なんで彼のことが好きなの？私は彼の良いところを見つけられないんだけど」
to have trouble ...ing で「…するのに困る・…できない」
ご参考まで！
カナダ 
