I hired a contractor who scammed me out of thousands of dollars on repairs to my flooded home (and have since located others he scammed). He has a green card and has applied for US Citizenship. How do I report his scamming to immigration so it is in his file when he goes to Citizenship hearing/interview?

I would first find a lawful way to get my money back, like small claims court to start. It's also an easy thing to get the contact information for the agencies you think could help, including immigration services with a Google search.