かな

Combination of か (ka, interrogative particle) +‎ な (na, mild exclamatory particle).[1]

First attested in the late-Edo period as an apparent shift in sense from the Old Japanese and classical usage, wherein the な (na) came to express more a sense of mild doubt rather than admiration[1] (see that section for more).

かな • (ka na) 

1. [from early 1800s] expresses a question with a feeling of worry

   彼(かれ)は怪(あや)しい人(ひと)かな。 ― Kare wa ayashii hito ka na. ― I wonder if he's a suspicious person.

   まあ、そうかな。 ― Mā, sō ka na. ― Well, maybe so.

2. expresses skepticism: really?, is it?
3. (in the form ～ないかな (...nai ka na)) expresses affirmation: I hope, I wish
4. expresses confusion

From Old Japanese. First attested in the early 700s.[1]

From か (ka, particle indicating doubt or uncertainty) +‎ な (na, mild exclamatory particle).

Displaced particle かも (ka mo) around the early-Middle Japanese stage.[1][2]

かな • (ka na) 

1. [from early 700s] (Classical Japanese or literary) expresses wonder or postulation on the part of the speaker

   善(よ)き哉(かな)！

   Yoki ka na!

   Wonderful!

Still used in contexts that deliberately evoke a classical or literary sense, such as poetry.[2]