It occurs in the orthographies of Jacaltec (a Mayan dialect), Malagasy, Tol language, and Cape Verdean Creole, in all four cases representing a velar [ŋ]. It is also used in the Boruca language, Nawdm language, and Ocaina language.
"N̈" and "n̈" appear in very few languages, so they are not represented on any computer keyboard in any language.
Neither "N̈" nor "n̈" have precomposed forms in the Unicode character set, meaning their only representation is as a combining sequence of a letter "N" (or "n") followed by a combining diaeresis U+0308.
"N̈" and "n̈" are not available as HTML entities.
In popular culture
The letter is probably most commonly known for its use in the title of the fictional band Spın̈al Tap. Its use there parodies the metal umlaut used gratuitously by several actual bands, such as Blue Öyster Cult, Motörhead, and Mötley Crüe. According to fictional musician David St Hubbins, "it's like a pair of eyes; you're looking at the umlaut, and it's looking at you".
The video game Borderlands 2 contains a boss named Captain̈ Flyn̈t.