Clueless
clueless /ˈklulɪs/
adj. 一无所知的;一窍不通的;(对某事)不懂的，无能的
It means that someone knows nothing about a particular subject or he/she is incapable of doing a particular thing properly.
它指的是某人对某事一无所知，或不能正确地做某件事。
I am as clueless as everyone else about why he did this.
我和大家一样对他为什么会这么做，一无所知。
She is totally clueless about physics.
她对物理学一窍不通。
