Why can't you say siapa kursi ini.
Siapa kursi ini = Who is this chair
And what would mean 'Kursi ini siapa'
"Kursi ini siapa ?" = "This chair is who ?" / "Who is this chair ?"
How about "Kursi ini milik siapa?"
'Kursi ini milik siapa?' means 'Whose chair is this?'
Kursi ini milik siapa? Whose = milik siapa, yes no?
Something is wrong with this sentence. May be it is better to say, Siapa yang milik kirsi ini?
Siapa yang milik kursi ini ? Who owns this chair ?
It seems more natural to me too
"Ini adalah kursi siapa?" Isn't that okay?
Also who is this chair?
"Who is this chair ?" = "Siapa kursi ini ?"
But that is a strange sentence, both in Indonesian and English.
"Siapa" ("Who") is a question word that is used to ask about a person.