
Simply ask your vet to refer you to an expert in the use of scanners. There are some vets who are well trained in using this as a diagnostic tool.
If the retained test*cle is found to be lying above the inguinal ring it will be unable at this stage to pass down, but if it is below then it may well still descend.
There is no hurrry to have the retained one removed either as it is just that there is a greater risk of cancer in it being in the wrong place, it isn't inevitable or likely to happen very quickly.
Franklyunless it is a breed where the coat alters unacceptably I eould wait until your boy is fully grown and looking like a male before having him fully castrated if the teste doesn't drop, as with one he will be unshowable so you may as well have them both off to prevent even the remotest chance of him procreating and passing the trait on.