Final answer:
Playing the piano is the activity that most clearly demonstrates mixed dominance related to ambidextrousness because it requires both hands to perform complex tasks simultaneously.
Step-by-step explanation:
The activity that most clearly demonstrates the type of mixed dominance related to ambidextrousness is playing the piano. When playing the piano, both hands are required to perform complex and often independent actions. This requires the brain to control fine motor skills in both the dominant and non-dominant hand simultaneously, which is a clear demonstration of mixed-hand dominance or ambidextrous abilities. Activities like shooting a basketball or signing a contract typically involve a dominant hand, while doing jumping jacks involves symmetrical movement and does not highlight mixed dominance.