Kosmos & Atomos - start by opening one hint at a time to see if it's enough information
If you haven't found the other snow angel, besides the one hanging on the wall, try looking at the floor in front of the main entrance of this building, in the south-eastern area of the Campusarea. The location of the "lying" angel is marked by a red dot in the picture below.
Try lying on the floor and imagine the lamps in the ceiling above are stars. Then simply count them.
The number of lamps/stars is 17
The answer to this riddle is therefore 17