I am using 2 extruders. Is it possible to use them both at the same time. Now I can use one at a time but not both at the same time. Is there a gcode that supports this action?
To print with 2 extruders simultaneously you need a firmware that supports that. Luckily, there is a firmware called Sailfish that is able to do that. The feature you are looking for is called
Sailfish firmware is found here
That depends what you want to achieve. If you want to get a clone of your thing then - 0scar answer is a go for it.
In early days, I was thinking that this could speed up my printing, if both extrudes could work simultaneously - a piece here, a piece there on the same layer. But then I realized that this will be a good source of oozing (even with retraction a nozzle can touch already printed area by another nozzle) so my printout could get material drops.
Moreover, in most cases, we don't want to have one color printout scratched by another nozzle as that also decreases quality and visual outlook of printed thing.
From hardware point - there could be more strain on the CPU to drive next stepper (depends on the solution) and that can lead to slower printing alltogether.
If you want a ditto printing is not mandatory to have a specific firmware (or g-code), you only need to add extruder to your end effector and - because of electrical power requirements - add further stepper driver for further stepper motor. Please note that the maximum footprint of your printed object is less than the extruders distance, for obvious physical reasons, therefore is not that common to see, the typical dual extruder goal is to use different filament/color. Of course, you have to achieve a notable calibration skill, and of course you have to modify the electronics of your printer (but this can be done quite easily, you only have to share the enable/step/dir signals with all the stepper driver). This has been already done with the MPCNC project.
Otherwise, if you want something more flexible, there are commercial printers with independent extruder. This one, for example
Edit: i can't comment your answer yet, but can you describe your current 3d printer setup? Because if you have the two hot ends that are only few mm apart it makes little sense to ditto-print something.