It can be replaced with kashira かしら (used mostly by women).
1. At the end of sentence
電車に間に合うかな。
Densha ni ma ni au kana.
I wonder if I will be in time for the train.
彼女も来るかな。
Kanojo mo kuru kana.
I wonder if she will come, too.
これでいいかな。
Kore de ii kana.
I wonder if this is all right.
2. After (adjectival) noun (+ na no なの)
これは誰のかばん( なの )かな。
Kore wa dare no kaban (na no) kana.
I wonder whose bag this is.
(na no なの after the adjectival noun is often dropped)
3. After conjunctive form of verb + temo ii てもいい
窓を開けてもいいかな。
Mado o aketemo ii kana.
I wonder if it's okay to open the window.
