Great question!!! As far as evidence goes, we have folk lore and even a chapter in the Bible (Job chapter 41) which describes a leviathan which sounds alot like a dragon.
As far as scientific evidence goes, there isn't really any that I'm anyway supports the existence of dragons whatsoever. Dragons for all intents and purposes where just made up to serve as a deterrent for people who wanted to go on certain quests in the days of old. Theyve never really existed.
The term dragon is originally of Greek decent, stemming from the word "draconta" which means to watch, and this suggests that they were meant to guard something. This explains why in almost every fairytale about dragons they are always tasked with the job of protecting something, be it treasure or weapon or princess.
Yes, dragons have roots in alot of cultures all over the world and there was a time when people even supposedly found dragon bones, but it wasn't until the discovery of dinosaurs that people realised that dragons never really existed.
Well whatever the case, scientific evidence or not, I somewhat like the concept of dragons, fire breathing creatures with majestic wings and bullet proof scales which could breath fire and sometimes even ice!! There's no way someone as imaginative as me wouldn't like them.
Dragons never really existed at least we haven't found any scientific evidence to support that they did. Hopefully we'll never have to come across a dragon in our lives because I don't know about you but they sound extremely terrifying.
I hope this helps.