KanjiJLPT N1
Cavity

cavity, hole, slit, very, great, exceedingly

Mnemonic

A child picks his nose so aggressively he bores a deep cavity right through the nostril — a perfect round hole you can see daylight through. His mother shrieks, but the child just shrugs and peers through the cavity in his nose like it's a tiny telescope.
Additional thoughts
Picture the kid's finger drilling into the nostril until it pops through, leaving a clean circular opening. The absurd image of a child using his own nose-cavity as a spyglass locks the radicals together.
Quick recall
A child drills through his nose, creating a perfect cavity he uses as a telescope.

Details

The keyword for 孔 is cavity. This kanji refers to a hole, opening, or hollow space, often one that occurs naturally or serves a specific function. It can denote any kind of aperture or passage, from tiny pores to larger openings. The character also appears in the name of Confucius (孔子), though its core meaning centers on the concept of a physical cavity or opening.
On'yomi
こう、く
Kun'yomi
あな