I'm not sure what I should do改为同义句
I'm not sure 【what to 】do.
我不确定该做什么?为什么用to do ?在宾语从句中，特殊疑问词+ 主语+ 谓语动词，可以缩写为特殊疑问词+to+谓语，比如：I don't know how I can go there.=I don't know how to go there.