Ian-san, anomalous58-san,
こんにちは!
Thank you, anomalous58-san, for advice! It's quite close!
In English, "play the guitar" and "know how to play the guitar" are the most common expression, while
we Japanese consider it as "skill" or "ability". So we use potential form 弾ける in such questions.
When we ask "does anyone play guitar?", we say 誰かギターを弾ける人はいますか。
We start the sentence with 誰か because we don't even know whether or not anyone plays the guitar.
If we know someone in the group plays the guitar but we don't know who, then we say ギターが弾けるのは誰ですか。
誰か is really "does anyone..."
Natsuko(奈津子),
Team JapanesePod101.com