The GPU Profiler is similar to the CPU Profiler, with various contributions to rendering time shown as a hierarchy in the lower panel. Select an item from the hierarchy to see a break-down of contributions in the right-hand panel.
Note that on macOS, GPU profiling is only available under OSX 10.9 Mavericks and later versions.
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.