"Do I not swim?"
Translation:Zwem ik niet?
https://www.duolingo.com/skill/dn/Questions-1/tips-and-notes Where did you not see the conjugated part of the verb switched with the subject for a question?
You have to use the right form of the verb for the pronoun you are using. Scroll down to Indicative mood Present tense conjugations of zwemmen:
No, there is another verb form for present continuous, which can also be put in question form.
"I don't swim?" in English isn't really a question as much as surprise at what I just heard which may not be expressed with a question in Dutch at all. In English we are really asking , "Did I hear you correctly?" Maybe my next words will be "Of course, I can swim!" Maybe in Dutch you might ask, "Did you just say I don't swim?" in Dutch though.