Can somebody tell me the Minecraft command to clear an entire world and destroy every block if u Dunno please don’t answer >-

You can't, but..

Explanation:

You cannot "clear" an already existing world.

But you can create a new one, click on "More world options", then click on "world type" until it says "superflat", and then you can click on customize and there you can remove every layer, therefore making the world to not spawn with blocks.