read somebody's face 察言观色

“察言观色”，汉语成语，字面意思是“carefully weigh up a person’s words and closely watch his/her facial expressions”，指观察言语脸色来揣摩对方的心意。可以翻译为“watch a person’s every mood或read somebody’s face”。

例句：

她善于察言观色，能领会经理的心思。

She is good at gauging people's mind, and so she understands the manager's every mood and thoughts.