nosebleed
衂 centers on bleeding from the nose: a nosebleed.
衂 combines 血 (blood) with 刃 (blade), suggesting blood from a blade, which fits the nosebleed meaning. The exact historical development is uncertain.
Blood 血 and a blade 刃 together: imagine a sharp blade causing a nosebleed.
For ジク, imagine a jigsaw puzzle piece shaped like a nose dripping blood: jigsaw -> ジク, and the blade 刃 cut the nose 血.