丈二和尚，摸不着头脑
zhàng'èr​hé​shang​mō​bu​zháo​tóu​nǎo

at a total loss

Senses

丈二和尚，摸不着头脑/ 丈二和尚，摸不著頭腦 zhàng'èr​hé​shang​mō​bu​zháo​tóu​nǎo at a total loss

To be completely baffled or unable to make head or tail of a situation; literally describes being unable to touch the head of a monk who is two 丈 zhàng (about 6.6 meters) tall.

References

see 丈二和尚，摸不着头脑/丈二和尚，摸不著頭腦 → 丈/丈