YOU SAID:
I now what you do last summer
INTO JAPANESE
私は今あなたが昨夏何をするか
BACK INTO ENGLISH
What do you do last summer now
INTO JAPANESE
去年の夏は今何をしていますか
BACK INTO ENGLISH
What are you doing last summer
INTO JAPANESE
去年の夏は何をしていますか
BACK INTO ENGLISH
What are you doing last summer
That didn't even make that much sense in English.