It's very rare to be pretty and not know it.
If you have to ask if you're attractive chances are you are most likely average. People always say, "maybe you're attractive and people are intimidated". Possibly, but for majority of people you're more likely to be average than overly attractive.
If you want to test it out walk up to the most attractive person you know around you and offer to walk with them. If you are average you will notice a significant difference in how people treat you. I did this with one of the most attractive woman I've ever met (dark skin petite East African woman with a gorgeous face) and walking with her around campus solidified how it's very rare for an attractive person to not note it. Women were over complementary with her and men stared A LOT! When anyone I knew walked up to me they'd insist on introducing themselves to her and wouldn't stop staring at her even if you are the one that's speaking. Generally when I walked with anyone else I always had to introduce them first and whenever I walked with friends and we crossed someone I didn't know but they did no one would ever insist on introducing themselves to me and they would only ever stare at my friends. Men especially forget you exist when you are standing next to an attractive woman.
There is no way any person who is attractive doesn't know it. So many women would tell her how pretty she is. It just doesn't make sense for an attractive person not to know it. So if you have to question it you may just be average like majority of people. But one thing I've noticed is that for women, you can create what I like to think of as "artificial attractiveness". If you're slim/ fit and dress well A LOT of people will perceive you as attractive enough. If you wear immodest clothing a lot of men will perceive you as attractive. But a woman with a gorgeous face and slim body will always stand out the most no matter what. That's what I've just noticed.