分かんないんだけど

何が言いたいのかさっぱり分かんないんだけど。

I have absolutely no idea what you're trying to say.

何が言いたいのか分かんないんだけど。

I don't know what you're trying to say.

意味が分かんないんだけど。

I don't understand what it means.

どのバスに乗ればいいか分かんないんだけど。

I don't know which bus I should take.

何が悪いのか分かんないんだけど。

I don't know what's wrong, though.