For today's lesson topic, we'll discuss the different German ways of saying that you "have no idea" about something, or admitting you just don't know. The simplest way, of course, is to say ich weiß nicht, but let's look at some more interesting options, starting with one that you must already know:

Ich habe keine Ahnung, wie ich das der Person sage,

I have no idea how to tell the person

Caption 49, Deutsche Welle: Leben zwischen zwei Kulturen in Namibia

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Occasionally, you'll also hear ich habe keine blasse Ahnung, which translates as "I haven't the faintest idea."

...obwohl er keinen blassen Schimmer hatte, wer das sein sollte.

...although he ​​hadn't the faintest notion as to who that could be.

Caption 36, Märchen, Sagenhaft: Der gestiefelte Kater

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The literal translation of blasser Schimmer would be "pale shimmer" or "pale gleam," but it's a German idiom similar to the English expression "the faintest notion" or "the faintest clue."

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Der hat voll die Peilung.

He completely understands.

Caption 21, Filmtrailer: Free Birds

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The noun die Peilung means "bearings" or "soundings," as in "keeping your bearings" and not getting lost, but here it is being used in a figurative sense. Thus, if you negate the sentence above and say ich habe keine Peilung, it means that you don't understand.

Ihr Name ist Hase. Ihre Kreditkarte wird Ihnen per Post zugestellt.

Your name is Bunny. Your credit card will be delivered by mail.

Caption 22, Kein Kredit: im Land der Klone

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The above is a play on words in the video: a customer calls a bank asking for a credit card for her pet bunny, and the automated response is "Your name is Bunny." This has a double meaning, since the idiom Mein Name ist Hase is slang for "I don't know" or "I have no idea."

Also, ich verstehe nur Bahnhof.

Well, I don't understand anything.

Caption 27, Die Pfefferkörner: Gerüchteküche

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This phrase suggests a foreigner in Germany who only understands the German word for train station—which is one of the first words that a visitor to Germany learns. It is especially appropriate when you don't understand the details of a particular topic that somebody is discussing.

Further Learning
Go to German Yabla and find other examples of the phrases discussed above to get a better feel for the contexts in which they can be used.