How do I make a command block destroy some glowstone?
You can use the
/setblock command to replace the block with Air.
/setblock <x> <y> <z> minecraft:air destroy
<z> are the coordinates of the block you want to replace.
destroy is an optional parameter that determines how the block is broken, in this case meaning that the block that was there would be destroyed as if it was destroyed by a player.
More information on the
setblock command can be found here: Minecraft Wiki