Answer:
If you cannot reach any points of the background layer, check whether the settings for the object snap are correct.
If all other points are detected by object snap, the problem arises when importing the background layer. If two lines do not lie exactly in one plane, even if these planes are only separated by an infinitesimally small distance, no node is created during the import. Thus, this intersection point cannot be selected. Therefore, you should solve this problem directly in your DXF file.
