No, Denmark cannot do that. Denmark does not own Greenland.

Greenland has a parliament and manages its own domestic affairs. Denmark manages some domains like foreign and defense policy, but Greenland governs its own territory.

They could but they'd say that's not what the people of Greenland want. They don't want to be an owned territory when they're used to their autonomy. They don't want their land exploited for minerals and oil by the highest bidder. They don't want to be made a military target between the US and Russia.

I'm not saying there isn't a deal to be made but it's got to be with the people of Greenland.