Is there any application note describing how to implement USB suspend mode (entering and exiting suspend mode) on Kinetis MCU?
There are no App notes that I'm aware of. Can you be a bit more specific about what you're trying to achieve? Are you a USB host or device? Are you using a USB stack? Baremetal or RTOS?
As a device, for example, you could use Freescale's baremetal stack, and it will handle suspend for you. Stack version 4.1.1 added an example implementation for the TWR_K20D50M to the hid_keyboard example, that will put the device into STOP mode after the host issues a suspend.