1)
Between what two gates was David?
1.
Radak: The city had a wall within a wall, and a gate within a gate. There was a place to sit between the gates, like it says above (4) "El Yad ha'Sha'ar."
2)
Why did he go on top of the gate?
1.
Malbim: He happened to go on top of the gate, and he was able to see Achima'atz. Had he continued looking through the gate, he would not have seen him, for he was coming from the side.
