Home | Clipboard | Select, dropdown: Connection, click a net. This will mask everything except for the net.
To clear the mask in Schematic:
On the ribbon: View | Schematic | Clear Masks - [Shift+C]
If you use Tools | Find and Replace | Cross Probe and click a schematic component, the PCB will be masked except for that component. It can then be seen easily and selected, edited, etc., without affecting other objects.
To clear the mask in PCB:
On the ribbon: View | Highlight & Edit Mask | Clear - [Shift+C]