How to view monitor refresh rate in macOS?
You need to hold down the option-key while clicking the "Scaled" radio button to bring up the hidden part of the interface.

However, usually this does not give you any information on Refresh rate on this type of monitor as you cannot set it anyways. 

You can click the Apple-logo in the top-left corner of the display, choose "About this Mac" and then "System Report" to bring up the system report. Choose "Graphics/Displays" and you'll have the information on the monitor. In the listing "Resolution" you'll see the refresh rate.