略知皮毛

lüèzhī-pímáo

[smattering; have only a superficial knowledge of a subject] 比喻稍有一些表面、 肤浅的认识

何况我们不过略知皮毛, 岂敢乱谈, 贻笑大方!--清·李汝珍《镜花缘》