I have a question about my characters responding to my oponent´s characters...

Can I respond with my Cersei´s Attendant if my opponent´s Cersei Lannister is killed? (It doesn´t read "After YOUR Cersei Lannister...")

Cersei´s Attendant

Response: After Cersei Lann ister or Cersei's Attendant is killed, choose and kneel a character.

Yes, it´s possible to trigger the response when your opponents Cersei Lannister is killed.

Ok. Thanks.

That´s what I supposed but I wanted to be sure.

Note, however, that you cannot trigger your copy of Cersei's Attendant if your opponent's Cersei's Attendant (or another one of your copies) is killed. That's because whenever a card uses its own title as part of its effect, the rules say that it is only referring to itself. So Cersei's Attendant can use its Response when any Cersei Lannister is killed (regardless of control), but not when any Cersei's Attendant is killed - just itself.