You have in front of you a shuffled deck of cards, face down. You get to choose a card from any position. Which card should you pick to maximize your chance of selecting the second black ace from the top.
Select the last (52nd) card.
Proof
Each position has an equal chance of being a black ace (since the deck is well shuffled). However, for all but the last card, some of the probability is that it is the first black ace. Thus the last card has the highest probability of being the second black ace.