STRAIGHT ANSWER
Which nakshatra am I born in?
Your janma nakshatra is the lunar mansion the Moon occupied at your birth, it sets your first dasha, your name-sound, and half of every compatibility score.
HOW JYOTISH ANSWERS IT
The real method, not the superstition.
It takes your birth date, time and city, the Moon's sidereal longitude resolves to one of 27 nakshatras and its pada. The finder also returns the gana, yoni and nadi facts and the syllables tradition assigns to that pada for naming.