Hi 你好！！！！ 想請問back in hong kong yet，　即係點解？？？　已經返咗香港定係將會返？？？

看似是英語人問你(或通訊的對象)"back in hong kong yet?"
假如是這語境，意思是問你「是否(回來)在香港？」或「回到香港未(沒有)？」。正確文法的全句可能是"Are you back in Hong Kong yet?"或,"Have you returned to Hong Kong yet?"

假如是對方表達自己去向的一句句子的尾....I'm not back in Hong Kong yet.意思是「未回到香港」，見到yet通常的語境都是"否定"的，一般是指未完成，未到時間，還未到等等。

yet (adverb) is in negative and conditional contexts(back to HK correct) indicating ignorance or uncertainty after not=not yet.
eg:-They are not here in HK yet=Not yet here in HK.
eg:-We have had no news from them yet.
eg:-We have not yet had news from them yet (from usa.).
eg:-Even now they had not yet decided how to go back to HK !
eg:-I wonder whether they have bought the CX air tickets yet .
eg:-Have they arrived yet=Back to HK yet ?

yet=一會兒前
所以他在一會兒前返回。

Are you come from hong kong?
When you back to hong kong?

我覺得是 還沒回香港

未返

只有back to , 錯文法，但港人不計較，亦會明白

已經回到香港

The answer is OBVIOUSLY asking IF you've come BACK TO hong kong from wherever you were at

are you back in hong kong yet?
你回到香港了沒有?