Who does 3 John say "has received a good testimony from everyone"?

Answer: Demetrius

"Demetrius has received a good testimony from everyone, and from the truth itself." The elder adds his own testimony too.

“Demetrius has received a good testimony from everyone, and from the truth itself. We also testify for him, and you know that our testimony is true.”— 3 John 1:12 (BSB)