Female or Male?
It is hard to sex a dragon before they are 12 months old. Baby dragons go through huge grow spurts and their bodies frequently change. I have had some babies that I could tell the day they hatched if they were male or female and others it was a best guess. Even in bigger dragons I have had the experience of purchasing a sub-adult from other breeders and we both thought the dragon was female and it wasn't until after over 1 year we realized she was in fact a he. This is very common in the dragon breeding community if you are only looking for a specific sex you might want to purchase a juvenile or sub-adult instead of a hatchling.
But How Can You Tell?
To sex the dragon you need to lay the dragon on their belly with their rump facing you. GENTLY lift the tail up and back. If your dragon is Male you will see two long parts on either side of the tail and a 'dent' at the tail base. If your dragon is female you will see no 'dent', instead a small bulge at the base.
You can follow the video example below to sex your dragon:
The first dragon shown in the video is a Male, the second is a female
Female or Male?
It is common to hear that you can sex a dragon based on if they have "enlarged" pores. But unless you have lots of different dragons to compare to this is difficult and "enlarged" is open to interpretation. New dragon owners sometimes think just because they have pores they are male, this is not the case as both sexes have pores around their rump. My advice is to not use this as a basis for sex determination.