I am not sure which to buy？I am not sure 是我不确定后面加一个宾语从句主语为I，谓语为am not sure 宾语：which to buy which to buy？相当于宾语从句，是疑问代词加不等式构成宾语从句希望可以帮助您
sure后面是宾语从句= I am not sure which I should buy.
