For this question, we can just easily list down the possible outcomes of rolling a number cube twice. In this case, since the list is already given, we can easily find which is the missing outcome.
If you notice, for every first outcome, there is a corresponding outcome of each number from 1 - 6. Analyzing the list, we can see that there is no 3,3 from the list, which is one possible outcome of rolling a die twice.
Therefore, the answer would be 3,3.