You will need to create a new question for the comment box. There is no option to add a comment box to a array question. But what I don't understand: You have the comment box already there. How did you get it there in the first place?
One other thing: What I also think is strange is that you are using check boxes and not radio buttons for this question. From the question I can see that only one answer per row should be allowed, but the check boxes would allow more than one.
(Se quiser, também podemos conversar em Portugues, mas no forum portugues então. Mas sempre melhor aqui no Ingles, porque tem muito mais pessoal para responder).
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Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.