Do frogs have a sense of smell
Absolutely. If you find a picture of its brain you'll find what's called an "olfactory bulb." This is the area of its brain that recognizes image input from the nose. The frog's olfactory bulbs may even be comparably sizable to those of humans!
Yes. They have a smell organ on the roof of their mouth called the Jacobson's Organ.
Yes, but I don't think it's as strong as some animals.