in oblivia ruins in the middle after a quest where you have to face it in the past you get it in the first thunder temple on s rank with 10 percent chance (im still trying to get it) from a friendly soul who spotted this by a error (im dk so dont remember how to say it corect
a rock go squad member have the 52nd quest
Ask someone else!
After you defeat lucario and obtain the blue gem, a quest will be avalible to save a piplup from a pokemon.
you are too old for such foolish games
take the quest from the old man in the cabin on mt.sorbet
Go to serebii.net to find out. That is what I used to figure it out.
if that quest is the 51st quest you've done,or you have completed all the quests,go to aqua resort,and you'll get a quest from a go-rock squad member.you need to find his sister and brothers.you actually can get lucario later on. p.s if you played the pokemon ranger game that is in the fiore region,you'll find out that the go-rock squad is actually the criminal gang that you need to defeat in that game.but they say the're from the almia region.
in a quest only at Pokemon ranger 2
The 51st quest in Pokemon Ranger Tracks of Light is called "Electric Energy for Panema".
If you have EVERY SINGLE pokemon in Guardian Signs, including Lucario, you go to Rand's House. There you will be given a quest, to get the last pokemon. I won't tell you anything about it, so it will be a surprise :). If you already have done that, I suggest doing the in-the-past temple missions, the ones you got from seeing Celebi. If you've done all those too, and found the slates, I'm not sure.
ranger net wi fi
It is near the Daybreak Ruins, you need a Pokemon with smash abilty *1 to knock the fruit out of the tree. Give the fruit to Booker, and then you have Quest Clear.