Translation:I do not hear well in my right ear.
"I don't hear well in my right ear" also sounds correct to a native English speaker. Just as in English one would say "I don't see well out of my right eye". Yes, it's technically correct to say "I don't hear well with my right ear" or "..see well with my right eye" but "in" and "out" seem to flow with the innate directionality of the senses.
I am a native English speaker, and "I don't hear well with my right ear" sounds more natural to me than ". . . in my right ear." I don't think I have ever heard anyone use "in" with this sentence structure, though I have heard, "I have hearing loss in my right ear."
Now Duolingo doesn't accept "I don't hear well with my right ear," at all. Therefore I protest and have reported it.
I would typically use 'with my ear' in this context but would perfectly understand 'in my ear'.
Collins French-English dictionary says 'de' can mean 'with', which matches like what Duo is teaching in this example.
Je l’ai fait de mes propres mains. I did it with my own two hands.
So I interpret this lesson as: Je n'entends pas bien de l'oreille droite. I do not hear well with my right ear.