は分からないな

I don't know

→ は
phrase Rare #26,726
I don't know A conversational way to say that something is unknown or unclear to the speaker. The sentence-ending な adds a reflective or casual tone. In related expressions such as 意味はわかるな?, わかるな? means “you understand, right?”
JA: 彼が来るかどうかは分からないな。
EN: I don't know whether he'll come.

フランス詩人のことは分からないな

I don't know much about French poets.

ロシア語は分からないな

I don't understand Russian.