
"How do I
spot ..." :D Love it! :D Seriously, it's not easy. It's not possible to tell whether a pup will be a top winner because there are so many things that can change between 8 weeks and adulthood. You need to know the standard well and to be able to visualise how each pup will develop and compare that mental image with the standard.
Study the pup - check to see if it has the correct mouth for its age. Make sure it has no hernia. If a dog pup, see if both testicles look as though they're on their way down. Make sure its tail isn't too short (quite a common problem) and that its not carried too high. Have a look at it moving - not easy as pups tend not to move in a straight line! The ideal spotting (though of secondary importance to correct construction) is evenly spaced over the animal, with the spots on head, legs and tail (uncommon but desirable) smaller that the ones on the body. Ideally the ears will also have plenty of white on them. Make sure his eyes are brown or amber (if he's liver) and that his nose and eyerims are filled in. You're also looking for an outgoing character. Also, 'top winners' are likely to be bred from so it's vital that he's been BAER tested and has a certificate proving this.
Hope this helps - there's more, but that's a start.
:)