I don't think one is in the cards, but it goes without saying Denmark couldn't do squat to stop it.
They don't have any way to get their poorly equipped (e.g. they gave away the last of their artillery to Ukraine) brigade to Greenland.
If the U.S. took it, there wouldn't actually be a fight.
But if Greenland becomes part of the U.S., it won't be the same way the United States acquired territory including present-day California, Nevada, Utah, New Mexico, most of Arizona and Colorado, and parts of Oklahoma, Kansas, and Wyoming, which was ceded after conquest from Mexico through the Treaty of Guadalupe Hidalgo (1848).
It would be a treaty concession, like the Louisiana Purchase (1803), Spanish concession of Florida (Onís-Adams Treaty of 1819), Oregon Treaty with Britain (1846), or the Alaska Purchase (1867).