Originally a mixture of the 終助詞（しゅうじょし） (sentence ending particles)
か, and な,
かな evolved over time to become its own (singular) sentence ending particle, which roughly translates as ‘I wonder if (A)?’.
As it is a sentence ending particle,
かな can be added to the end of almost any sentence.
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あの人（ひと）が道（みち）の真（ま）ん中（なか）で倒（たお）れてるけど、大丈夫（だいじょうぶ）かな。
That person over there is laying collapsed in the middle of the street, but I wonder if they are okay.
-
このコンロにこの魚（さかな）が入（はい）るかな？
I wonder if the fish will fit in this stove.
Combining the meanings
か and な, we can see where
かな gets its original meaning.
か presents questions (usually to other people), while な shows that a statement is related purely to the speaker’s own thoughts/opinions. In this way,
かな expresses that the speaker's own thoughts are being questioned.
In the past,
かな was thought of as being a fairly feminine way to express ‘I wonder’, and males tended to use phrases like
だろうか to express the same type of statement. However, in modern day Japanese,
かな is used by both men and women equally.
-
この通帳（つうちょう）はお母（かあ）さんのだろうか。
I wonder if this is my mother's checkbook. (Slightly masculine)
-
あの人（ひと）は本当（ほんとう）に弁護士（べんごし）なのかな。
I wonder if that person is really a lawyer. (Commonly used by anybody)