How to kill a dragon?
This may be helpful: https://wiki.guildwars2.com/wiki/Victory_or_Death#Walkthrough
Good luck.
Clear the adds whilst the dragons fly around and then when they hover in front of the ship, jump on the cannon which is nearest to it and attack. Shouldnt really be anything else to worry about from memory.
You don’t need to see the reticle to shoot at it and shouldn’t need to see it to select it either – just click in the area you know it appears (aka the dragons neck) and it should still select. As long as you’ve got the dragon selected as your target that’s where the cannon will fire.
You can keep firing for the entire time the dragon is hovering and it will hit, regardless of whether you can see the reticle or not. The only reason to stop firing during that time is to apply the shield to reflect his attacks – which does help a lot because then you’re not standing in a cloud of poison.
And as Randulf said you can use the time while he’s flying around to clear the other enemies so you’re not getting attacked so much while fighting him. If necessary skip a round of attacking the dragon to clear them – you can’t run out of time in this fight.
“Life’s a journey, not a destination.”