"Where is my sister?"
Translation:Dov'è mia sorella?
When the possessive refers to a singular noun indicating kinship, such as: "padre" (father), "madre" (mother), "fratello" (brother), "zio" (uncle), etc...
But... - With "mamma" (mom) and "papà"/"babbo" (dad) the article is required. - The adjective "loro" is always preceded by the article. - If the noun indicating kinship is altered, the article is always required. - When an adjective of quality and the possessive refers to the same noun, the articles is always required. See http://www.arnix.it/free-italian/italian-grammar/possessive-adjectives-in-italian.php