What is degenerative myopia? can a retinal specialist determine in high myopics if his/her myopia is degenerative?

Not all have it: This is a condition in which in the presence of higher degrees of myopia (not very common) there are changes at the back of the eye near the areas that see fine detail in which the retina may stretch, develop pigment changes and sometimes bleed. It is very, very uncommon and most myopes, even extreme don't have this. Any ophthalmologist can find this if present and the best steps can be taken.

Severe progressive: Nearsightedness. In some cases the features of degenerative myopia can be easily identified. In other cases it may be more difficult to ascertain. Some retinal specialist rely on serial b scans while others use exam findings. My guess is that you will find variety of ways to both classify and also diagnose high myopia. Not always an easy diagnosis!