あの女の子は誰だろう。

あの女の子は誰だろう。

I wonder who that girl is.

あの女(おんな)の子(こ)は誰(だれ)だろう。

Ano onnanoko wa dare darou.

彼の (あの、かの)

that (someone or something distant from both speaker and listener, or situation unfamiliar to both speaker and listener)

女の子 (おんなのこ、おんなのコ、おんにゃのこ)

girl

は (は)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

誰 (だれ、たれ、た)

who

だ (だ)

be; is; indicates past or completed action; indicates light imperative

Readings: ジョ、ニョ、ニョウ、おんな、め

Meanings: woman, female

Readings: シ、ス、ツ、こ、 -こ、ね

Meanings: child, sign of the rat, 11PM-1AM, first sign of Chinese zodiac

Readings: スイ、だれ、たれ、た

Meanings: who, someone, somebody