Final answer:
The joint space that should be open for a well-positioned AP oblique knee projection with medial rotation is the medial and lateral tibiofemoral joints.
Step-by-step explanation:
The correct answer to the question 'Which joint space should be open or almost open for a well-positioned AP oblique knee projection with medial rotation?' is the medial and lateral tibiofemoral joints. This choice correlates with the anatomical structure involved in the AP oblique projection of the knee, specifically focusing on the condyles of the femur and the tibia. Proper positioning of the knee for this type of imaging should display an open or almost open space at these articulations as the femur undergoes slight medial rotation when the knee is in full extension.