Some questions (major spoilers)

2) What was the significance of the scar?
It symbolized his muteness.

3) Did his father die at the end, or was he merely in a state of shock?
Dead.

4) Why did Dylan's mother kill herself? Were there any clues in the movie as to the reasons for her committing suicide?
No, which is why Dylan thought he might be to blame.

5) What was the significance of the shattered glass door fixing itself?
Lets you know there is no escape from the apartment.

6) What was the Djinn up to? Seemed like he was reanimating spirits and let them run rampant throughout Dylan's house.
No. It was assuming the shapes of the dead, as is mentioned explicitly in the book of the dead. That's why the mother form was blind after Dylan had sprayed RAID into the old man's eyes.

I think wrlord was on point with everything except Q #3.

I was under the impression that the Djinn made Dylan’s father mute in exchange for giving Dylan a voice. I did not think that his father died at the end. You could see that his father was trying to speak but he could not. That would make more sense in terms of the Djinn perverting his wish than simply killing the father. But I guess it isn’t totally clear. Maybe you could think that his father was killed by the Djinn?

Oh, and good movie by the way. So little in terms of dialogue but it still has a fully fleshed out story with suspense and emotion. I really liked this one.

Hi! I watched the film recently and enjoyed it a lot. Glad that there is a discussion about it here.

I think the film could have been interpreted either literally (the Djinn was real and everything we saw was real too) or symbolically (there was no Djinn and everything we saw was Dylan dealing with his guilt and fears); if it was not for the last sequence, which basically rules-out the second possibility. Therefore, I believe that we should stick to the literal interpretations.

Now to answer the questions:
1) Judging by the shape of his scar, I say a lung surgery, or a similar surgery related to his respiratory system.

2) Maybe to give the audience a clue as to why he is unable to speak. Dylan was not deaf, so I believe his muteness had a physical reason. He was also rather fluent in sign language, so I don't think his muteness was because of the shock of the suicide, since it happened only a few months before. Rather, it was because of a physical impairment, or the surgery itself (It could have also been a symbol of his guilt if the film would have gone for the symbolic interpretation).

3) No. The father just lost his ability to speak. When the Djinn is strangling him, his "voice" leaves his mouth and enters Dylan's. This also fits well with the notion that the Djinn twists the wishes. So, for exmaple, if Dylan would have wished for his mother to return, the Djinn would have probably killed his father. But now he just made him unable to speak.

4) I think there is no definite answer. It might have been due to Dylan's muteness (which he also believes to be true, which is quite sad), or it could have been for other reasons.

5) Literally to show that Dylan could not run away from the house. If the film did not rule-out the symbolic interpretation, it could have meant that Dylan's belief about being guilty for his mother's suicide was so strong that he couldn't escape it so easily. He had to beat the Djinn/guilt to be able to escape his house/psyche. But as it stands, I think it was only there to show that he couldn't escape the house.

6) Acoording to the book, it was going to kill Dylan, or "consume his heart". The thing is, the Djinn couldn't really do that (or do much of anything in this realm) without having a physical body, thus why it assumed the form of several people. What I don't get is why it was still trying to kill Dylan after midnight. He should have been unable to do so, I guess.

I hope this helps.