I don't know who that is / I don't know him (her) / I have never heard of that actor
What movies has he (she) been in? / What movies has he (she) appeared in?
Kamenashi appeared in movies called ~ and ~. He also appeared in Gokusen.
「その人は分からないなぁ」= I don't know who that is / I don't know him (her) / I have never heard of that actor
「どんな映画とかに出てる人?」= What movies has he (she) been in? / What movies has he (she) appeared in?
「亀梨はPとJKっていう映画にも出てるよ。あとはごくせんにも出てたよ」= Kamenashi appeared in movies called ~ and ~. He also appeared in Gokusen.
ボキャブラリー
「出ている・出演する」= appear(ed) in 映画・ドラマの名前 / be in 映画・ドラマの名前
「映画」= movie / film
「俳優」= actor
「女優」= actress
"I don't recognize that name. What other movies have they been in?"
「I don't recognize that name. What other movies have they been in?」という表現を使ってみてください。これは「その名前は分からないなぁ。他にどんな映画に出てたの?」という意味になります。
また、「亀梨は『PとJK』という映画にも出てるよ。あとは『ごくせん』にも出てたよ」は、"Kamenashi was in a movie called 'P and JK'. He's also been in 'Gokusen'."と表現できます。
なお、「recognize」は「認識する」、「they」は「彼ら/彼女ら」ですが、個別の男性や女性を指すときにも性別を問わずに使われることがあります。これは英語の表現として一般的に使われています。