Wing claw

[RamenDemon]

A single human finger/thumb is capable of breaking wood. Is a dragon's thumb scaled to equivalent its own size? Also, don't think the wings are fragile things. If they are fragile, they wouldn't be capable of lifting the dragon, which weights tons (or more) and ultimately binds the pitiful dragons to the ground (which also presents an answer to why they're gone).

Again, please use correct punctuation / grammar. ~Namhias.
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Really, you should know better than steal a bowl of ramen from a Dragon.. *slu-u-u-rp*

[Hyraxylos]

No the wings definitely aren't fragile. They can bash things around pretty heavily and inflict serious damage. It's often thought (incorrectly) that the wings are fragile because the majority of a non-feathered wing is the thin leathery part. But flying creatures that use their wings for fighting either slap each other with the flat or bash each other around with the "arm" part.
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The statement below this one is false.
The statement above this one is true.
This statement is false.

[Shiari]

Here is my reasoning for thumb-claws.

Pterosaurs had a special bone at their wrist, something rather like a spike. This bone was flexible in about a 90 degree range, and could either face perpendicular to the body or parallel. The purpose of this bone was to extend and manipulate the leading edge of the membrane that connected along the front of the wing-arm. Doing so provided extra lift and maneuverability.

The wing-thumb in dragons could provide a similar function. Wings are the hardest part for dragons to get right it seems. So it's entirely possible that the membrane could extend partway up the thumb without anyone remembering such a small detail.

In fact, aside from some manipulatory abilities, that was the function one of the two thumbs on each of my wings likely served.

[Obsidian]

My kind used it as a weapon.
Wingbones are very strong and somewhat flexible, and are driven by the biggest muscles in a dragon's body. With a suitably sharp spike on the end, it makes a lethal spear.
Its a very useful tool if you dont want to get your essential body parts close to something you are attacking, and dont have a breath weapon. The whole wing, tightly folded, could be used as a spear to inflict nasty stabbing wounds, or even pierce flesh, hook in, and drag a smaller victim into range of a bite.
Then again, my race are a primitive lot. Other races/species will obviously have other uses/biology/evolutionary pressures and will be different as a result.
But thats what ours were for.