Where can I find the complete list of Arduino Serial Command & Query Strings?
The Arduino has no "standard" serial commands.

It is a programmable device which you have to program yourself. The only serial commands it can respond to are the serial commands you yourself program it to respond to.

There are projects around that provide a serial interface, but they are generally designed for one specific purpose, and the commands or protocol they implement are unique to that project.

The closest to what you are asking for is the Firmata firmware, which comes with the IDE, and can be used to control the Arduino through the serial port using programs on your PC.