difficult [hard] to understand
〈言葉などが〉 unintelligible
〈字などが〉 illegible; hard to make out; crabbed.
He has no understanding
ハッキリわからぬ
よくわかりません
I cannot understand.
わけわからない。
I don't understand the reason.
to be frustrated because one finds something difficult to understand
よくわかりません。
わからないです。
to have difficulty understanding something
a tune which is difficult to understand
分からないよ。