Question: what are two dots over a vowel?
Answer: The diaeresis (/daɪˈɛriːsɪs/ dy-ERR-ee-sis; also known as the tréma) and the umlaut are two different homoglyphic diacritical marks. They both consist 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.