Command Explorer
This extension shows the group and menu identifiers of existing commands to make it easy to find out where to place your custom commands.
Download this extension from the Marketplace or get the CI build.
Open the tool window
Click on View -> Other Windows -> Command Explorer to show the tool window.
Use the filter text box at the top of the command list to easily find the command you're looking for.
Inspect mode
This checkbox allows you to point at any command in any menu, toolbar or context menu to select it.
Once enabled, you can now CTRL+Shift+Left-Click any command and it will select the command you clicked on in the command list.