I want to use Dunkleosteus to destroy Planetary defence but I don't know how to find coordinate. 
https://prnt.sc/r8fmyw

A Dunkleosteus does not have any guns to shoot with, it rams into it's enemies :D I do not know much about them, but I don't think they are good for taking down pirate OPS. They are better used to destroy other players stations and moons with. You need a space station with gravity gun, from human's moon to properly take down planetary defense and shields. https://prnt.sc/ra1bmy , https://prnt.sc/ra1bso