Two for men and dance, one for pairs and women.
The selection pool is determined by two minimum scores (ISU TES minimum and DEU minimum total score), and the skaters are then sorted by their three highest scores plus their Nationals score (I think?). Felix, for example, has just reached the DEU minimum score, but he doesn't have the ISU TES minimums, so he's currently not in the running for one of the two spots.
I think the three skaters in the selection pool following Nationals are Genrikh, Leon and Soner.