N-diaeresis
"N̈", or "n̈" (referred to as n-diaeresis or n-umlaut) is a grapheme from several minor extended Latin alphabets, the letter N with a diaeresis mark.
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.
Encoding
"N̈" and "n̈" appear in very few languages, so they are not represented on any computer keyboard in any language.
Neither "N̈" nor "n̈" are characters in the Unicode character set, and have to be represented as 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.
The video game Borderlands 2 contains a boss named Captain̈ Flyn̈t.