Where does “Jyotsna” come from?

Jyotsna (English) comes from Sanskrit ज्योत्स्ना, from Proto-Indo-Iranian *dyáwtsnaH.

Ancestry of “Jyotsna”, step by step

Step	Language	Word	Meaning
1	Sanskrit	ज्योत्स्ना	moonlight; a moonlit night; splendour, light
2	Proto-Indo-Iranian	*dyáwtsnaH	—

Jyotsna — Etymology, Origin & Word History | Etymology Explorer