Does Ahri Legend work on teammates battlefield in 2v2?

No, Ahri Legend's ability (Nine-Tailed Fox) does not trigger on your teammate's battlefield in a 2v2 game.

According to the RiftJudge FAQ (ID 9756):

"No, Ahri's legend ability (Nine-Tailed Fox) does not trigger when your teammate is defending.

According to the card text, the ability triggers 'When an enemy unit attacks a battlefield you control.' In the 2v2 format, you and your teammate are distinct players, and you each control your own battlefields. Therefore, an attack on your teammate's battlefield is not an attack on a battlefield you control, and your Ahri legend ability will not trigger."