"Just north of Vein Town in the Forest, there will be a man. Speak to him and accept his quest in order to get Cranidos. Go north towards the first bridge you will see. Before going onto the bridge, follow the path left into you go down and go near a tree. Once at the tree, you will see Cranidos being chased by a Wartortle. When they see you, Cranidos will run up to you and you will have to face both of them. capture them both and Wartortle will leave. Cranidos will join your team here and the quest will end" -Serebii
For Lumineon: If you did the Sharpedo quest that was required to move further in the game, then this quest is easy. Go back to where you found Sharpedo swimming around, and now, Lumineon will be following it.
Hope this helps.