It will show its sex when getting ready to flower. A common way to distinguish males is their height compared to other plants of the same strain, but from your question I presume there's only one plant. So, you're gonna have to wait until it switches to blooming :)
If this a photoperiod plant you want to be able to tell until you switch the light cycle to 12/12. But looking at the pictures it looks like it's going to be a female.