Working out if a talent is known
 

I'm trying to write a module to my addon for my Death Knight that shows a warning when the Icy Talons buff is about to drop off or is missing. Which I've done... BUT

If I don't have the talent then I'll never have the buff and thus the warning always shows.

Is there an easy way to detect whether the talent is currently known or not?

This might help
https://warcraft.wiki.gg/wiki/API_GetTalentInfo

But you might have to build up a list of current talents to make it easier to find a talent if the direct route doesn't work.

You could make the simple approach and only activate the message if Icy Talons had been actived earlier. It's dirty but simple :-)

Only problem is it won't work until you have actually cast the spell - and it won't work after you respec.