Why do you keep doing it when you know he/she doesn't like it?
Why do you keep repeating the same behaviour even though you know he/she doesn't like it?
「相手が嫌がると分かってることをなんで何回もするの」＝ Why do you keep doing it when you know he/she doesn't like it? / Why do you keep repeating the same behaviour even though you know he/she doesn't like it?
ボキャブラリー
why ＝ なぜ、なんで
keep doing ～ ＝ ～を繰り返す、～をやり続ける
he/she doesn't like it ＝ 相手（彼・彼女）が嫌がる
even though you know ＝ あなたが分かっているのに
If you know what you're doing bothers the other person, why do you keep doing the same thing over and over again?
この場合、次のような言い方ができますよ。
ーIf you know what you're doing bothers the other person, why do you keep doing the same thing over and over again?
「あなたのやってることが相手を悩ますとわかっているなら、なんで同じことをなん度もするの？」＝「相手が嫌がると分かってることをなんで何回もするの？」
to bother someone「人を悩ます・イライラさせる」
over and over again「何度も何度も」
ご参考まで！
イギリス 
カナダ 
