Satoshi knows Lance since It's from Kanto region champion. But it did not show on episode that they know each other or they had interaction before.
But anyway, this is really getting interesting now :)
This is what I'm talking about.
Korrina saying something like "as I thought Satoshi!, the battle with you is really exciting!" (base on the dialogue, it seems they already had a battle before)
and Satoshi replied " Could you show me Lucario's real power soon?" (base on this one, It seems Satoshi knows about Lucario's real...