1. Is it okay for me to open the door?
[Is 'It' a dummy subject? Is 'for me to open the door' the real subject?]
2. Is it okay if I open the door?
[In this sentence, is 'It' a dummy subject? Does 'It' refer to 'if I open the door'? Is 'if I open the door' the real subject? Or is 'It' a situation it?]
In questions, the subject and verb are reversed. In all these questions, "it" is that impersonal pronoun, to get the sentence or question going.
Statement: It is okay for me to open the door.
Question: Is it okay for me to open the door?