1. Where? In your city, county, state, country, or the world? Sentenced or pending trial? For state or federal violations?

2. Same thing. Also, since there is no clearinghouse for this information nor mandated-reporting, any numbers you might get are going to be highly speculative.

3. I’d suspect you’re going to run into the same issues as in #2 above. Particularly in those states where medical marijuana is allowed, people are probably not going to be running around advertising that they’re using it.
References :
In my 21st year of California law enforcement.