SuperLab 4 is designed around a single response–not composite responses. In order to retrieve two responses (other than string input), you must present two events, both expecting a response. You can configure both with the same set of correct responses and provide feedback.
The difficulty I’m having with any of the methods I’m coming up with, though, is that there’s no way to ensure that the second selection is different from the first. Therefore, the participant could click the same item twice, and both responses would be registered as correct.
If you’re just wanting to present an event as feedback after both responses have been given, you can use Macros. You’ll need to set up a code value on trials marking whether a trial is correct or incorrect. The trials would need to be set to “correct” by default. A feedback would need to be created to change the value to “incorrect” for both events retrieving a response. Then, you can set up a Macro that runs at the end of the trial that checks this code value. If the one previous trial is marked as incorrect, you can present an event notifying the participant. Unfortunately, this method still has the problem that it wouldn’t be able to differentiate whether the same response was given twice.