Ok, well you have to be careful heating things so that you don't get hurt. At a minimum please wear safety goggles.
But if you have a substance, and you think that the substance is relatively pure, you can heat the substance and notice the temperature at which it boils. It will probably be off by a bit if it is impure. The purer it is, the closer the boiling point will be to the literature values that I reported above.
If the boiling point is way off, it means that they sent you the wrong substance.
...do you own a fire extinguisher?
Edit: I just noticed that CBG boils at 248 degrees, I'm not sure that your stove top can safely heat much above that. Do you know how hot your stovetop goes to?
Edit: So basically you just find a safe way to heat it up and note the temperature at which it boils. I don't want to over-complicate it for you. The real issue is safety but if you're the sort of person used to cooking food at home you basically already have the requisite skills for this.