Does the "jumper plate" (1×2 plate with centered stud) have a Danish nickname like the "Erling"? Who is the designer of this part? And does there exist a catalog of designers of specific bricks?
I cannot find any cases of the Jumper Plate brick having a Danish nickname, the closest you might get to a Danish nicknamed would be a literal translation: jumper plade.
The Erling brick is a very rare case of a brick being named after its creator. I imagine most bricks created nowadays are produced by not one but several people. It's possible that such a catalogue of brick designers exists, but is not publicly available.
Although it is not a nickname, the official internal name of that part is 'Plate 1 x 2 with 1 Knob' according to Brickowl