don't know what to say
我不知道说什么好。
I don't know what to say.
— 隐藏摄像机 (2005)
这话说的我都不知道说什么好了
I don’t even know what to say to that.
— Hi, Mom (2021)
他不知道说什么好。
He doesn't know what to say.
不知道说什么好
— 春光乍泄 (1997)