Dogs don't like to eat truffles, though they can be trained to find them. If your friend's dogs haven't been truffle trained, there is likely something else attracting them to the tree. Maybe a dead animal is buried under the tree or an animal is roosting in the tree and dropping urine or scat under the tree.

Truffles species do grow in North America, mostly on the west coast, but their ediblility has not been established. See the link below for info

Here is a link that might be useful: Truffles

im not sure if truffles are found in pa but i know that the response from judy b should be ignored simply bescause they say in response that a truffles edibility has not been establised and yet it has been on the tables as a delicacy for centuries and is today one of the most expesnsive edible mushrooms there is
hope you find out if they can be found in pa im looking too lol almost listened to judy till she said they are not edible good luck

How do I know if a found truffle is not deadly?

There are hundreds of species of truffles, some native to the US, but most are not edible....or at least worthy of being eaten :-) Only 5 species are considered to be of culinary value. Although none are reported to be 'deadly' or toxic/poisonous, I'd still want to confirm an ID.

According the the Audobon Field Guide to Mushrooms,

"Not all underground fungi are truffles and not all truffles are edible, nor is any common European truffle know to grow in North America. Because North American truffles have not been systematically studied (except on the West Coast where they are relatively abundant and quite varied) the eating of American truffles cannot be recommended. Based on animal studies, however, no truffle is known to be poisonous . . Identification is extremely difficult for most species. . ."

But the fact that no truffles in Pennsylvania have been studied and that where they are studied identification is hard suggests that you don't want to eat anything you find.

I love mushrooms and I often pick them just to identify them. I've found that plenty of poisonous or deadly mushrooms have that delicious mushroom smell, so don't rely on smell to tell you if what you find is edible.