よけいなことなのかな。 I wonder if this is unnecessary.
もう朝なのかな。I wonder if it is already morning.
彼女は何も食べたくないということなのかな。I wonder if she does not want to eat anything.
世界遺産のことは今日の新聞に出ているかな。
I feel that these sentences are mostly used when you are talking to yourself.
They can be spoken by both men and women.