所在
しょざい · shozai · JLPT N1 · noun
whereabouts
所 — door 戶 (left) + axe 斤 (right)
Originally a sound: an axe (斤) chopping wood near a door (戶), with 戶 also hinting at the pronunciation. Over time it was borrowed to mean 'place' or 'location,' and later became a grammatical particle nominalizing verbs ('that which…'). The concrete 'chopping' sense faded entirely.
在 — earth 土 + phonetic 才
Originally a phono-semantic compound: 土 (earth) gives the meaning of a place or location, while 才 supplies the sound. It came to mean 'to be present/located at,' and now also serves as a grammatical marker for ongoing actions, like 'in the middle of doing.'