You can't look at a snake and just tell the sex, though, there are 4 ways of telling.
1- Popping
2- Probing
3- Spurs
4- Tail Lengths
Take out #3, since your snake is a colubrid and has no spurs (pythons & boas have spurs).
Popping is pretty reliable, IMO. I pop my snakes to tell the sex, and it works pretty well. Though, the only problem is that there is a risk of injuring the snake, so that's why research is your friend. Try looking up YouTube videos to see how other people attempt to pop their Corns, and also read up a bit on it.
Probing is another option besides popping. It works pretty well, but I wouldn't ever consider doing so unless shown how by a professional. The only bad thing about this is that if you push the probe in too fast or too hard it can damage the inside of the snake, which is not good at all. Best let a vet do the probing.
Tail lengths are not reliable unless compared with another male/female. Males have a much longer tail to be able to hold the hemipenes. The base of the tail is also thick. For females, their tale tapers a lot quicker because they have no space for hemipenes, resulting in the females' tail being short and quick-tapered.