Rogue Galaxy Quarry: The Seaside Terror
The closest save teleporter to use in order to reach The Seaside Terror is Nalvasa Sea - Midpoint. From here you'll want to head south and into the kidney shapped area on the map. In here is where you'll find the circle with the ?. If you're having trouble finding the location just check where I am standing on the map.
The item needed to summon this boss is Pirate's Grogg. It is a fairly common item after the halfway point in the game.
If you are missing the item required to summon this boss grind some battles and cross your fingers or go treasure chest hunting on a planet you've 100% the map on. In Rogue Galaxy once you pass a certain chapter the loot table of items that can drop for you ingame is updated.
What I mean is, every item has a chance of dropping off every creature after you've passed that chapter that allows that item to drop. At least this is how it works in my experience. Therefore, if you're missing any items to summon any of the quarry bosses all you need to do is grind a little until you get that item to drop for you. Good luck!