The callout.js file is not located in the local machine. It is located in the server where your SharePoint is installed.
For SharePoint 2013, it is located in:
C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\LAYOUTS
For SharePoint 2016, it is located in:
C:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\TEMPLATE\LAYOUTS
You don't have to locate the file. Just use the SP.SOD.executeFunc function to create your custom callout. Below is my demo code for your reference:
Test result:
Reference:
36851.sharepoint-2013-creating-custom-callouts.aspx
highlight-content-and-enhance-the-functionality-of-sharepoint-hosted-sharepoint