Who disscovers Denmark?

Denmark wasn't discovered in the same way as perhaps America. There is no danish equivalent to Christopher Colombus.

Denmark was probably discovered some 10'000 years ago when the glaciers of the last ice age melted away and the land could be inhabited. Tribes of hunters probably wandered into Denmark in search of prey, and humans have lived there ever since.
There might have been humans in Denmark before the ice age, but they would have been driven out by the glaciers.