"I can sleep on the sofa."
Translation:Mogę spać na sofie.
Tak, przyimek("preposition") na użyty z miejscownikiem("locative") opisuje miejsce "akcji".
(Yes, preposition "na" with locative is used to describe the place of "action"[i.e. where the verb takes place])
Not my first thought, as the sentence sounds to me rather like a guest saying that he can sleep there tonight, but yeah, technically it's possible that it will be regular/habitual. Added.
In previous lessons, musieć meant must, has to, or needs to, while umieć meant can. A Polish dictionary I have also uses these definitions. Now I see in this sentence, musieć is interpreted as "can". When is musieć used for can and when is umieć used?
No, that's not "musieć", "mogę" is a form of "móc".
"móc" (mogę) can mean that I am allowed to do something, that I am able to do something, etc.
"umieć" means that I know how to do something (and that's why I can do it). For example "Umiem spać na sofie" is possible, but rather unusual, and I guess it rather means that you are able to fall asleep on a sofa even though it's not the most comfortable place to sleep.