This can be tricky on appearance alone as varnishes used to traditionally be high-gloss whereas now, varnishes are available in satin, matt and ultra matt making them look more like an oil or wax finish. This said, and although not an exact science, there are ways to establish what type of finish a floor has.
Always
carry out these tests in an inconspicuous area such as behind a door or on the floor under a piece of furniture, as there is potential for the testing to leave a small mark or stain.
Scrape test
Using the edge of a coin or finger nail gently scrape the surface of the floor. If the floor has a wax or polish finish the scraping will remove some of the wax or polish and it will be visible on the coin or nail.
Oil test
Apply a small drop of cooking oil such as Olive Oil to the floor and leave for 30 mins to an hour. If the oil partially or fully soaks in to the floor then this is an indication that the floor has been oiled. If the oil droplet remains on the surface, then it is likely to be a varnished floor.