I reached lucario rank, but I still havent battled him... When will I?

You CANNOT battle or recruit lucario in mystery dungeon blue or red rescue team. There is a thousand different lies about tricks that you can do to see him but you can't. This game was made before the new set of Pokemon for sinnoh and they threw in the legend of lucario's greatness as a rescue team leader for added mystery and to give players a taste o the new Pokemon.(remember when this game first came out ppl didn't know who lucario is). It's the same concept with seein munchlax in the game- to give players a taste of the next set of Pokemon.

I have the mission to go to Dojo Registration where you guide Blissey to take it to another Blissey in my job list, but I cannot take the job how do I get into the Dojo Registration dungeon

Darn it, I can't believe this I fell for one lie that you can get Lucario or fight him but oh well, but this time won't fall for it and would just believe that people who got lucario hacked the game an order to recruit lucario and battle it. So yeah don't listen to those people who said that you can fight and recruit lucario.