了如指掌
liǎo​rú​zhǐ​zhǎng

to know something like the back of one's hand

  1. 了 瞭 liǎo verb
    to understand
    (bound form) to understand or know clearly; to be bright or clear-sighted; to comprehend
  2. 如 rú preposition
    to be like
    to be like; to be similar to; as if
  3. 指 zhǐ verb
    to point; to refer to
    to point at or to; to indicate; to refer to; to mean
  4. 掌 zhǎng noun
    palm
    (bound form) palm of the hand; sole of the foot; paw of an animal