How does Henry Gatz hear about the funeral?
Henry C. Gatz in The Great Gatsby sees that his son has died when he reads the Chicago newspaper. After he arrives at the house in the novel, we read:
"I saw it in the Chicago newspaper," he said. "It was all in the Chicago newspaper. I started right away."
He is then at the house, for the most part, with Nick until the funeral, so he naturally learns about it.
He shows great pride in his son's accomplishments, and disappointment when so few attend the funeral. He also echoes the title of the novel when he says that his son would have been a great man if he had lived.
As was mentioned in the previous posts, Nick Carraway receives a telegram from Henry Gatz telling him to postpone Jay's funeral until he arrives in New York. When Henry arrives in New York, he tells Nick that he learned about Jay's death after reading about it in a Chicago newspaper. As soon as Henry heard about Jay's death, he immediately left for New York. Nick mentions that Henry Gatz is extremely proud of his son's accomplishments and is in awe of Jay's beautiful home. Henry then reminisces about his son and tells Nick that Jay would have been a remarkable man if he would have lived longer. He even shows Nick a book with Jay's schedule and resolves written in the back, which illustrates Jay's determination to become a success. Unfortunately, nobody attends Jay's funeral, and Nick Carraway leaves New York shortly after Jay is buried.
Henry Gatz is Jay Gatsby's father. He does not exactly hear about the funeral until he gets to New York. I think what you are really asking is how he found out that his son was dead. The answer to that is that he read about the murder in a newspaper from Chicago (Gatz is living in Minnesota, but apparently saw a Chicago newspaper). Here is the passage where we find this out:
“I saw it in the Chicago newspaper,” he said. “It was all in the Chicago newspaper. I started right away.”
Henry Gatz sends a telegram to Nick Carraway asking him to put the funeral off until he, Gatz, can get there.