After I have the workers build the pit for the Titan on the island of my choosing, the Titan gets left idle once it defeats any enemy units it finds there. After that, it sits unused unless bad guys attack the island. How do I transport my Titan from the island it emerges from so I can attack the other players Titans?
You can't. Once a Titan's spawned, you cannot move it to another island. You just have to build the gate on the island you most want destroyed or trick the enemies into coming to the Titan somehow.