"Where am I allowed to smoke?"
Translation:Где можно курить?
Можно is a word only used in impersonal constructions. It requires Dative and literally cannot have the Nominative "я" in any role. If you imagine for a moment that this expression is a panel with holes of different shapes, it does not have Nomantive-shaped holes at all. Я, ты, он, она, кошка, мальчик etc. will not match any hole no matter how much you try to push them in.
Note that adding "мне" to this sentence will imply that you are talking specifically about yourself, while in reality smoking is usually allowed or not to everyone equally.