How would the results differ if you added sodium p-toluate instead of p-toluic acid to the two-layered mixture of?

That depends on the pH of the water layer. If the water layer is basic or rather just not acidic, it will be in the water layer. If the water layer is acidic, pH 4 or less, it will be in the ether layer. On the question of upper and lower, either has a density of less than one so it will be the upper layer.