Apple removed the ability to burn disc images from Disk Utility in OS X 10.11 and newer, and while that makes sense for many Macs that no longer have SuperDrives, CDRW, and DVD burners, for those who use an external burner, use disc drive sharing, or who do have hardware with a built-in SuperDrive, may find it frustrating to lose such a feature. But not to worry, you can still burn disk images and data discs in OS X El Capitan, and you can start the process either from the Finder or from the command line on the Mac.

Source: How to Burn Disc Images in OS X El Capitan Without Disk Utility (OS X Daily)