Using Google Earth's elevation figures, Paraguay's highest point looks to be Cerro Tres Kandu (827 m), at 25.54.05.95 S x 56.09.33.54 W.
The second highest elevation appears to be its neighbour, Cerro Pero (819 m.) at 25.54.01.35 S x 56.08.54.08 W.
Other websites (eg. amateur-hikers.com and peakbagger.com) support this order, though their figures are slightly different, ie. 842 m and 815 m respectively.