If there were a 4th spatial dimension and you could see in 4 dimensions, yes, you could see the inside of things that are enclosed in 3 dimensions. It wouldn't be like x-ray vision exactly though. Think about a sphere in 3d. It is enclosed. When you take 2d projections of the sphere by slicing cross-sections of the ball, from a 2d observer on that plane, they would also see an enclosed circular object. But from the 3rd dimensional observer looking down at that cross section they can see everything enclosed in the circle. From the 4th dimension, then it stands to reason they would have a similar view of a 3 dimensional objects innards. But rather than seeing through the object like in an x-ray, they just see the whole thing laid out in every detail at once like we see the insides of the 2d circle.