Cartridge dumping is pretty easy once you have the required hardware added or changes made to your C64/C128. A modified Kernal ROM usually is sufficient. Disabling the expansion port and re-enabling it during C64 operation by using an added switch is another common method.
A very well written and illustrated article named Dumping Cartridges on the Commodore 64 by Markus Brenner is nowadays defacto main page for this topic. Check it out!