This question bothers me since i began to play.
My prestige indicator says that i am loosing 1.5 for that, which should correspond to 5 claims.
But i am only aware of 2 of them.
So the question is : is there a way to know in which province those claims are, or am i supposed to click on every single of them to know if they are part of those claims ?
Going into diplomatic map mode with your country selected shows green stripes on any cores that you do not own.
Also, to narrow it down, you can go into the "Casus Belli" page of the ledger and sort by the type of casus belli. Those countries that you have the Reconquest casus belli against are those countries that own your cores.
If you formed Spain really early, you'll have a core that you can't even see: the Canaries.