It's actually an interesting subject, both Syrax & Vhagar are described as "she-dragons" which begs the question, why ? Clearly the other dragons, Meraxes for example, must have had a dick and because Vhagar and Syrax didn't they were classed as she-dragons. That's the only thing that makes sense to me anyway, well as much sense as dragon cock can ever really make.
I'm thinking they take on whatever gender is needed, when some magical union is to take place. Or, as Jeff Goldblum put it...
"I can see it. You have more of the north in you than your brothers."
I had not planned on spending my Sunday evening "boning" up on dragon sex, but hey I'm just going to roll with this in case there is a test later on.
Please describe (using diagrams where appropriate) the exact manner in which dragons are conceived. Points will be deducted for anatomically incorrect dragon genitalia.