First of all, you need to be VERY VERY observant as they are pretty skittish and will avoid human contact wherever possible. Secondly, it's normally a chance encounter when you do get to photograph a snake or two unless you are trained to "hunt" for these snakes and locate their habitats.
I used to see cobras pretty often in Amoy Quee camp at yio chu kang area, behind Nanyang poly and facing amk ave 5 there is this very big field/bush land and it's part of the camp area. We used to see so many cobras (black) there and they even appear in the drains and pavements. Kinda irritating cos we have to move away to avoid them.
I've caught wolf snakes at my workplace in amk and normally they are found in grassy areas or drains.