You can reach Kimolos by ferry or by high-speed ferry from the port of Piraeus through line Kithnos - Serifos - Sifnos - Kimolos - Milos.
The trip lasts 6 to 8 hours according to the type of ship you choose.
For more information:
PORT AUTHORITIES OF PIRAEUS 210 4226000
PORT AUTHORITIES OF KIMOLOS 22870 51332