Howto see disk I/O utilisation per process - iotop and pidstat not available in Homebrew on macOS
iotop is available in macOS/OS X itself.

iotop relies on dtrace though and you have to disable SIP in systems like El Capitan/Sierra to run dtrace.

Check man iotop for options and then execute iotop as root :

sudo iotop [-C] [-D|-o|-P] [-j|-Z] [-d device] [-f filename] [-m mount_point] [-t top] [interval [count]]