An important part of Double Deck Pinochle involves reading your partner's signals. One of the fundamental signals is the "ace-on-ace leadback".
A "leadback" is a signal to your partner when they have the lead - that is, they are the first player to play a card in this trick. They will keep the lead by playing the highest cards - probably aces. At some point, they will run out of aces to play, and so they will probably lose the lead to some other player. They would like to pass the lead to you, so that your opponents don't get a chance to rake in point cards. If you can give your partner a signal, they may be able to play a card which lets you take the lead.
In the screenshot below, B-4 (West) has led with an ace, and their partner T-1000 in the East has followed with an ace. That's usually a bit surprising when it happens.
If (1) or (2) are true, then you can pass the lead off to your partner by playing a low card in the leadback ace's suit. To elaborate: (1) If your partner has the remaining aces in that suit, then you can play a low card in that suit, knowing that your left-hand opponent (Adam in the screenshot above) cannot take the trick. (2) And if your partner has no more cards in that suit, then they can play a trump card, and take the lead that way.
So, if your partner plays an ace on the ace that you led, don't ignore it. Lead with a low card in that suit, and you will most likely pass the lead to them. You may want to lead with the king in that suit, if you have one. If you feel confident that your partner will take the trick, you will be giving your partner your own king - a point - by leading it. In addition, your left-hand opponent must play a higher point card - that would be the ten in this case - so your team will very likely get 3 points out of such a trick. If you have no king in that suit, then lead a queen, which will also force your left-hand opponent to play a point card.
Here are some links to discussions about the ace-on-ace leadback:
There's a fun Double Deck Pinochle tutorial at World of Card Games. You can also find Double Deck Pinochle tips at Pagat.
This video demonstrates the ace-on-ace leadback in a hand of Double Deck Pinochle.