Is your son blind? The IRS
explicitly allows the deduction (under Medical Expenses on Schedule A) of
"guide dogs, including the cost of maintaining them". See IRS Instructions for
Schedule A.
If your son is not blind but is merely training such dogs, then he normally would not be able to deduct his expenses, unless he is doing this for a recognized charitable organization, in which case the following applies: "Contributions can be in cash, property, or out-of-pocket expenses you paid to do volunteer work for the kinds of organizations described earlier." (same instructions, page A-9). These would be entered under "Charitable contributions".
See "Examples of Qualified Charitable Organizations" in the link above to see if the organization he is volunteering for is qualified.