Hi
Noticed this plane this morning, can anyone explain what they are doing?
Notice the altitude.
One possibility is they could be doing touch and go landings.
They are circling burning off fuel while trouble shooting a problem in anticipation of an emergency landing.
The altitude readout in either case appears bogus which is more common than it should be.
Keep in mind that ADS-B reported altitudes are uncorrected pressure altitudes; zero doesn’t necesssarily mean ground level or sea level.
Hi
They actually returned to Copenhagen, so maybe it was just an inspection of the airport for some VIP’s 
Such Pattern can be because they maybe calibrating VOR for angular accuracy. That is required periodically.
From the looks of the picture you posted, they appear to be doing circles.