When the LORD met Moses at a lodging place on the way to Egypt, who circumcised Moses' son?

Answer: Zipporah

Zipporah cut off her son's foreskin with a flint (KJV: a sharp stone), and the LORD let Moses alone.

“But Zipporah took a flint knife, cut off her son’s foreskin, and touched it to Moses’ feet. “Surely you are a bridegroom of blood to me,” she said.”— Exodus 4:25 (BSB)