As you play games and finish tasks in MyTeam,
you earn points and currency that allow you to unlock players or buy card packs. Eventually you will unlock a player that has another NBA player as part of a Dynamic Duo
. An on screen help prompt will pop up when you unlock ONE of these players, telling you which other star is part of the duo. In order to get this achievement, you have to play a game with BOTH players on your roster. You can do that while editing your team line ups in the MyTeam
Here is a comprehensive list of the Duos:http://www.vhpg.com/nba-2k-dynamic-duo-cards/
It is important to note, that not all the cards of a player are actually part of the Duo, even if it is the player listed with a duo partner. There are different "styles" of cards and this achievement will only unlock if you have the "Duo" style of that player card. Having a regular or "possessed" Lebron card for example, will not work with a Duo card of Chris Bosh. Both players must be the Duo version. You will recognize this by seeing the 2 men with a triangle and arrows in the top left of the card. This indicates a duo card.
The easiest way to get this achievement is to:
1) Wait until you unlock 1 of these through packs, then buy the other player card in auction house.
2) Buy both players in the auction house.
You should get 1 of these players within the first few packs you open, maybe even before you play your first game.