Anything added using certain [Registration functions] gets added to one or more of the global [Registered definition tables].
Note that in some cases you will stumble upon things that are not contained in these tables (e.g. when a mod has been removed). Always check for existence before trying to access the fields.
All nodes registered with
minetest.register_node get added to the table
If you want to check the drawtype of a node, you could do it like this:
local def = minetest.registered_nodes[nodename] local drawtype = def and def.drawtype