〜かな・〜かしら
I wonder
Plain form + かな (feminine, older: かしら)
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かな at the end of a sentence means "I wonder": 明日、雨が降るかな, "I wonder if it'll rain tomorrow". It's か (question) + な (musing), often said half to yourself.
It follows plain forms directly, including nouns (雨かな) without だ.
With the volitional, it's thinking aloud about what to do: 何を着て行こうかな, "hmm, what shall I wear?"
With a negative, it's a wish: 誰か手伝ってくれないかな, "I wish someone would help".
かしら means the same and is heard in older and more feminine speech. The polite equivalent is でしょうか.
Register: Casual, often said to yourself. Politely: でしょうか.
Examples
明日、雨が降るかな。
I wonder if it'll rain tomorrow.
田中さん、もう着いたかな。
I wonder if Tanaka's arrived yet.
これ、おいしいかな?
Is this any good, I wonder?
何を着て行こうかな。
Hmm, what shall I wear?
誰か手伝ってくれないかな。
I wish someone would help me.
明日は晴れるかしら。
I wonder if it'll be sunny tomorrow.