Dobby’s full name is never explicitly mentioned in any of the Harry Potter books, Pottermore, or the films. Throughout the series, he is simply referred to as Dobby, without any additional surname or family name.
J.K. Rowling, the author of the Harry Potter series, did not provide a last name for Dobby or any other house-elf. It is important to note that house-elves in the wizarding world are often only referred to by their first names. This is a common practice that is seen with other house-elves as well, such as Winky and Kreacher.
In the books, Dobby is introduced as a house-elf working for the Malfoy family. He later becomes a loyal friend to Harry Potter and other members of the Order of the Phoenix. Despite his significant role in the series, his name is consistently mentioned as Dobby, without any additional surname.
It is worth mentioning that the lack of surnames for house-elves could be a deliberate choice by J.K. Rowling to emphasize their subordinate status in the wizarding society. House-elves are often treated as servants and are not granted the same level of individuality or recognition as wizards and witches.
Dobby’s full name is never revealed in any canonical materials. He is known simply as Dobby, without any additional surname or family name.