In general, you can find the source of any Contextual Task Bar shortcuts with the following steps:
1. Know the name of the option. A lot of times this can be done by reading the tool tip that appears when you hover the pointer over the option (if that hasn’t been disabled).
2. Choose Edit > Search, and enter the name in there. The Search panel lists everywhere in Photoshop where that might turn up (menus, tools, etc.).
This is not always so straightforward when they’re not specific commands or tools. For example, in the picture you posted, the tool tips for the three icons are Modify Mask Feather and Density, Hide Mask, and Change Mask View; Myra Ferguson already did a great job of explaning the very different places where those already exist outside the Contextual Task Bar.
The only thing I’ll add is that Overlay is actually more like selecting the layer mask in the Channels panel while the RGB channels are still visible. The point of Overlay is to get a mask preview that looks a lot like the rubylith masks that used to be cut by hand with a knife in traditional prepress, before digital editing existed. Many people prefer to see this view using the traditional Photoshop shortcut of pressing the \ (backslash) key. So it’s similar to Quick Mask but not exactly, because although Quick Mask has the same red overlay color, it’s more of an editing mode than a different view.
AdChoices