1st question:
One way to find out would be to open a popular ADS-B/Mode-S mapping application and sit and watch it for some hours. Let us know how you get on.
I know of aerodromes that are NOTAM'd closed which are allowing specific movements depending on circumstances. Therefore, the question is almost impossible to answer, really. .
2nd question
Hardly any, probably. I know of a couple for commercial schools which were very late to suspend ops, but using method as above (until I got bored) hasn't shown any activity recently. Concentrate on the popular commercial training aerodromes in your search. All the smaller PPL outfits, as far as I'm aware, are waiting patiently until someone comes up with a viable way of protecting their customers.
TOO