Trump doesn't need an invasion plan for Greenland. The US already has a treaty that allows it to occupy one base and to build and use others. But he doesn't want to do anything by agreement. He wants to dominate, but only when it's easy.
Trump wants to invade Greenland because he is weak and addicted to shows of dominance. He wants to invade it because he thinks it would be easy, it would destroy the coherence of NATO, and allow Trump to declare himself a Roman victor.