Final answer:
The positive test likely prompting the recommended exercise by the physical therapist was Ober's test on the right side, which indicates tightness in the tensor fasciae latae and iliotibial band.
Step-by-step explanation:
If the physical therapist recommended an exercise involving standing with the right side of the body next to the wall and the right arm resting on the wall for support, with the right leg placed behind the left in an extended, adducted, and externally rotated position, while the pelvis is shifted to the right and there is a slight trunk lean to the left, the test that was MOST LIKELY positive for the therapist to recommend this intervention would be the Ober's test on the right. Ober's test assesses the tightness of the tensor fasciae latae and iliotibial band, which can lead to hip and knee problems. By placing the leg in this specific position, the exercise aims to stretch these areas and correct the identified issue.