GPU-Z is not available for Mac but there are a few alternatives that runs on macOS with similar functionality. The best Mac alternative is The OpenGL Hardware Capability Viewer, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to GPU-Z and three of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to GPU-Z are Systempal (Paid) and CheckMyMac (Paid).
SystemPal is becoming an ALL-IN-ONE app. It is the best tool to monitor your memory/CPU usage status, CPU temperature and fan speed, network speed. It also provides a tool kit including mini music player, screen shot utility, memory cleaner.