意味わかんない
He has no understanding
I can't say what his motive is.
わけわからない。
I don't understand the reason.
よくわかりません
There are cases when I don't know that meaning.
わからないです。
I can not say for certain.
I didn't know that meaning.
I don't know about that kind of thing.
よくわかりません。
That just doesn't make sense to me.