We use "perilla" for the round doorknobs, because they remind the shape of a pear. For the lever kind, we tend to say "manija", which is also the handle of some drawers.
"Picaporte" is not very used, but it refers to all kinds of doorknobs.
If you say "pomo", we also understand the round kind, but very few people use the word.
As for the other meanings of "pomo", when it means a bottle of an alcoholic beverage, it's slang and not a very nice word to use among all kinds of people. When it's some kind of "frasco", it's usually like a pot of cream (a cylindrical container in plastic, metal or glass) "Frascos" here, are usually taller and bigger than "pomos", and always made of glass.