Why do you want to know if you are an expert? Just for personal validation or because a pattern dificulty said it was for experts?
If it is for personal validation then Suzeeq is probably dead on.
If it is for a pattern, then just try it. If it is too confusing or you have to look up how to do to many of the abreviations, then you may not be experienced enough yet.
WOW, I just realized that by Suzeeq's definition above I would be advanced, but I am most definitly a beginner (only knitting since February, self taught by youTube and the videos here) in my mind!! Yet I can figure out my mistakes, can fix them (although somtimes that means froging back to my lifeline and starting over), and am not afraid to tackle anything as long as it looks like fun. I also spend a lot of time looking up videos of how to do stitches, and a LOT if time Froging and tinking.
I started with simple garter stitch scarves, and now I am doing socks (My brother asked me to make some for him for Christmas) and a fair isle scarf (It looked interesting) as well as scarves with drop stitches, scarves with decreases and increases, scarves with repeated patterns.....
Maybe I should learn to do shawls, or sweaters next.
As far as deciding when you are an expert. I think it depends on you. When you Feel you know enough that you could reasonably answer anyone's questions without alot of trouble. That is when you are an expert IMHO.