Разобрался) спасибо
answers_controller.rb
def create
@question = Question.find(params[:question_id])
@answer = @question.answers.build(answer_params)
@answer.user = current_user
if @answer.save
flash[:notice] = 'Ваш вопрос успешно создан'
redirect_to question_path(@question)
else
render 'questions/show'
end
end