Examples I know. in Russian examples

How do I translate I know. into Russian?

I just don't know what to say.

Не знаю, что и сказать.

I just don't know what to say.

Я даже не знаю, что сказать.

I don't know if I have the time.

Я не знаю, есть ли у меня время.

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I know | I Know Who Killed Me | I know that I know nothing | I Know What You Did Last Summer