You can select edges, curves, etc… behind objects like surfaces, solid bodies if “Allow Selection of Hidden Wireframe” activated. The command is on the Top Border Bar.
If your selection problem goes on, look “Selection Scope” and “Type Filter”.
- Change selection scope as an “Entire Assembly”
- Change type filter as “Curve” or “Edge”.
Note: In larger assemblies, you might have performance problems if this command activated and “Edge” selected in “Type Filter”. Because mouse cursor will try to select edges behind objects when you move the mouse cursor on the screen.