what is the name of the two dots over a vowel
Diaeresis (diacritic) The diaeresis (UK: /daɪˈɪrɪsɪs/[citation needed], US: /daɪˈɛrɪsɪs/ dy-ERR-i-sis; plural: diaereses), also spelled diæresis or dieresis and also known as the tréma (also: trema) or the umlaut, is a diacritical mark that consists of two dots ( ¨ ) placed over a letter, usually a vowel. When that letter is an i or a j, the diacritic replaces the tittle: ï.[1]