when is に used to mark the subject?


I was reading a grammar book, and I stumbled across the following sentence

> 君になんかわからない

At first sight, I thought it means "I don't know you." But the translation
given beneath the sentence is "You don't know."

The subject of the sentence is totally different. In my previous experience, に
is always used for object mark as in "彼女に会いたい”, in which に is used for
indicating a receiver of the action.

So I gone to look up dictionary, and it does mentions some circumstance where
に is used as a subject mark, but it doesn't give details. So can anybody
clarify this usage or can provide some reference?




Various verbs like わかる and できる historically describe the quality of a thing.
わかる is perhaps better thought of as _" to be understandable"_. In this case,
the noun marked with に is the thing **by which** the subject of わかる _" is
understandable"_.

In your sample sentence, the subject is omitted (implied), and is presumably
whatever the speaker was talking about. This subject _" is not understandable
**by** you"_. This becomes _" you don't know"_, with "you" as the subject,
only in translation -- grammatically, in the Japanese, 君【きみ】 ("you") is not
the subject.

