Refer to IRS Publication 502 Medical and Dental Expenses.
Page 8 discusses Guide Dog or Other Service Animals.
A portion of such expenses are only deductible if you itemize deductions.
If SSI and SSDI is your only income then you do not even need to file a tax return.
I believe the statement "If SSI and SSDI is your only income then you do not even need to file a tax return" is not true in all cases. It is probably true in most cases - but not all. There are multiple situations where Social Security is your only income, but you may need or want to file a tax return. Some of those situations are for lump sum distributions, or if you receive a large amount of Social Security income, or if you had taxes withheld - you may want to file to get a refund. And yes, there are more such situations.
I suggest using the IRS Interactive Site to determine whether or not such payments are taxable
I further suggest using the IRS Interactive Site to determine whether or not filing a tax return if required.
For each of the above sites click the "Begin" button at the bottom of the screen.
SSI is not reported on a tax return.
If you had enough income for your disability benefits to be taxed, then you probably wouldn’t qualify for SSI anyways, as they are meant for low-income applicants.