The question "What specific good work are you accusing Jesus of?" is a sharp challenge in John's Gospel, but it does not prove that Jesus is God. At most, it shows that some opponents treated his words as blasphemy, while his works were recognized as signs of divine favor.
Why Christians find the argument strong
The argument comes from John 10. Jesus is threatened with stoning after saying, "I and the Father are one." He then asks, "I have shown you many good works from the Father; for which of them are you going to stone me?" They answer that it is not for a good work, but for blasphemy, "because you, being a man, make yourself God."
Stated at its strongest, the argument says this: Jesus' enemies understood him to be making a divine claim, and Jesus did not simply say, "You misunderstood me." Instead, he pointed to his works as evidence. So, the Christian apologist argues, the charge was not moral wrongdoing but the identity he claimed - and the miracles supported that claim.
What the passage actually proves
Even if one grants John's wording for the sake of argument, the passage proves less than that. The statement of hostile opponents is not automatically a correct interpretation. Prophets were often accused of blasphemy, sorcery, madness, or rebellion when they challenged religious authority.
Also, Jesus' reply in the same passage does not read like a simple affirmation, "Yes, I am God." He cites scripture where others are called "gods" in a limited, non-literal sense, then argues that calling the one whom God "sanctified and sent" the "Son of God" should not be treated as blasphemy. That is a defense based on agency, consecration, and being sent by God - not a plain definition of himself as the Almighty.
The words "I and the Father are one" can also mean unity of purpose and mission. In John 17, similar language of "oneness" is used for the disciples. No one thinks the disciples become one divine being. So the phrase alone cannot carry the full doctrine of incarnation.
How Islam reads Jesus' good works
The Quran fully honors the miracles of Jesus. It does not deny his purity, prophethood, or mighty signs. It explains their source: Allah empowered him.
"I have come to you with a sign from your Lord: I make for you from clay the form of a bird, then I breathe into it and it becomes a bird by Allah's permission. And I heal the blind and the leper, and I bring the dead to life by Allah's permission."
Quran 3:49
This is exactly the key distinction. A miracle proves that God supports His messenger; it does not prove that the messenger is God. Moses split the sea. Abraham was saved from the fire. The Prophet Muhammad (PBUH) was given the Quran. None of that turns a prophet into the Creator.
"The Messiah, son of Mary, was only a messenger; messengers had passed away before him. And his mother was truthful. They both used to eat food."
Quran 5:75
What it does and does not establish
The argument does establish that, in John's Gospel, Jesus' opponents objected not to his healing or mercy but to what they took as an unacceptable religious claim. It also establishes that Jesus' works were central to his defense.
It does not establish that their accusation was true, that Jesus taught the Trinity, or that miracles equal divinity. The Quranic reading is coherent: Jesus was the Messiah, born miraculously, supported by great signs, and sent by Allah - but he was not Allah.
So the honest answer to the question is: they were not accusing him of a specific good work. They were accusing him of blasphemy. But an accusation of blasphemy, especially from opponents, is not the same thing as proof that Jesus claimed or possessed God's essence.