minetest.register_on_dignode
From Minetest Developer Wiki
Syntax
minetest.register_on_dignode(function(pos, oldnode, digger))
Description
Called when a node has been dug.
Example
minetest.register_on_dignode(function(pos, oldnode, digger) print("Node " .. oldnode.name .. " at " .. minetest.pos_to_string(pos) .. " dug by " .. digger:get_player_name()) end)