I have just installed gnu-prolog using brew install gnu-prolog. When I try to run gprolog in the terminal I get gprolog: command not found. I tried doing the same to my other machine that is running ElCapitan and all worked perfectly.
Is there a way for me to get gprologto work for macOS Sierra?
Sounds like an issue with your Homebrew installation. But you can also install GNU Prolog using MacPorts or by downloading its Mac OS X installer from its website.