Three dragons by name are known:
The first yclept Glaurung,
Another was Smaug,
Who was I?
Ancalagon?
Scatha?
(see below)
Tolkien named four dragons in his writings: Glaurung, Ancalagon the Black, Scatha. and Smaug. As Glaurung and Smaug are mentioned in the riddle, it has to either be Ancalagon or Scatha.
Someone please try both answers and contact us with the correct one.