Doesn't and does not make sense; cannot means it is impossible for the duck to sing, and would require a different word. Cannot is able to be used in the present tense, though.
My assumption for the use of cannot would be "En and kan ikke synge", but I would need confirmation from another clever Duolingo member :)
A Rabbit entered a shop and asked: "Do you have carrots?". They said, "no we don't have." The following day the rabbit came to the shop and asked again, "Do you have carrots?" They replied angrily, " We said we don't have carrots, if you come back again asking for carrots, we gonna SINK A NAIL in ur HEAD with a HAMMER!" The third day the rabbit came yet again and asked, "Do you have a hammer? They replied, "NO." He said, "What about nails?" They said, "NO." Then he calmly asked, "Do you have carrots?" In this 2021 don't let the devil scare you, he doesn't have anything.
Best wishes n Warm regards , To start a new week on Happy Note ...