[knc1]

There should be output on the serial port, even with a dead eMMC chip -
That is, the first part of the initialization is run in the SoC's internal ram from code in its internal rom.

Re-check your serial port connections.

The thread about recovering a Kindle with fastboot has many logs attached to its posts, see those for what to expect. (the thread has 'fastboot' in its title, search for that).