The taskmanager from a Windows Hyper-V host only shows CPU and memory usage from the underlying OS. There is no chance to get information about the usage within the VMs running on top of this Hyper-V host using this single pane of glass.
Veeam, once again, helps you with another free-of-charge tool, the Veeam Task Manager for Hyper-V. This tool originally is part of the new Veeam Management Pack v7 for System Center but is also made available as separate download. Did I mention it's for free?
The tool will help you in troubleshooting ressource related problems on your Hyper-V hosts by displaying vital information about your host and your VMs in a task manager style.
You can get more information and download location here at Veeam's website.