I believe this question should be a multiple choice question as there are infinite number of solutions.
Some of these solutions are (2 cards whose sum is -12):
-12 and zero
-11 and -1
-10 and -2
-9 and -3
-8 and -4
-7 and -5
-6 and -6
1 and -13
2 and -14
3 and -15
4 and -16
5 and -17
6 and -18
7 and -19
8 and -20
9 and -21
10 and -22