Where is the point of relief when a golf ball is near the green behind a bush and the backswing is restricted by burn of the cart path?

If by "burn of the cart path" you're talking about a grassy hill that either frames the cart path or that the path is on top of, nothing. Play it as it lies, or take the consequences of declaring an unplayable lie . If your stance or swing is impacted by the paved surface of the cart path, then it's the nearest point of relief not closer to the hole.