Is it one ear or both ears to qualify for the deaf exemption?

What deaf exemption?   Is that a state thing?

yes in Arkansas

You might wish to consult this TurboTax article for helpful information:  Tax Tips for the Deaf

Arkansas provides the following information:
You can claim the Deaf Credit only if the average loss in speech frequencies (500 to 2000Hertz) in the better ear is 86 decibels, I.S.O., or worse. Any taxpayer age 65 and over not claiming a retirement income exemption on Line 17 is eligible for an additional $26(per taxpayer) tax credit.