Is it possible to find all my questions which have answers from specific user?
I would like to see if I forgot to accept some of his answers.
Search only acts on one user.
The search for all your open questions with at least one answer and is unaccepted is
user:104103 answers:1 hasaccepted:no closed:no
There's no syntax for "where question is by X and answer is by Y"
Only that user complains. My opinion it that my feedback is adequate to response
Feels problematic - While you aren't obliged to select an answer, you also shouldn't be selecting answers only cause users complain.
There's an implicit social contract for people to select the answers that worked for them, and a certain understanding that 'asking' people to select their answer as the correct one is not very classy.
Selecting an answer also keeps community from bumping up your question periodically. So, meh, if you need to go through your answers, you have about 150. Its worth reviewing them.