How do I disable context menu key from Windows Keyboard?
Provided you are not running macOS Sierra (which from a previous question, I know you are). Support for Sierra is promised to come.

Install Karabiner.

Run it and on Change Key tab search for "Application Key" (or navigate to "For PC Users" -> "Change PC Application Key (Menu Key)".

Select the mapping "Application Key to Control_L".



To disable completely you'd have to edit ~Library/Application Support/Karabiner/private.xml (examples). The key code (reference) is PC_APPLICATION, so the following line will add a menu entry:

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;item&gt;
    &lt;name&gt;Disable Windows context key&lt;/name&gt;
    &lt;identifier&gt;private.disable_windows_context_key&lt;/identifier&gt;
    &lt;autogen&gt;__KeyToKey__ KeyCode::PC_APPLICATION | ModifierFlag::NONE&lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;


(press "Reload XML" in Karabiner window to apply after editing the file)