The second subquestion should only appear after the user answered the first subquestion. Thereby, it is not relevant how the user responded. The second subquesiton should appear in either case.
The terms "question group" and "subquestion" are technical concepts in LimeSurvey.
I got the impression that you might use them differently for your question.
I currently don't understand your question. Perhaps others get it.
For a better understanding, I attached the question below.
This is a matrix question with two subquestions.
I want the second subquestion to appear only after the user answered the first subquestion. Thereby, it should be irrelevant how the user answered. The second subquestion should appear in either case.