Chances are, nobody will ever in your lifetime on a conscious basis. This is an unfounded worry, relax. Also ETs have more serious things to do or ways.
You'd have to be very open psychically to be aware of it happening. However, anyone capable of reading thoughts or remote viewing has a lot of spiritual power, which is fairly easy to detect. Even if you can't see auras yet, just speaking with a powerful person is usually enough to feel their aura's power, and also tell if they're a friend or enemy.
However, even if you can't detect these "psy spy" attacks, you CAN defend against them with a strong aura of protection. That works even if you can't observe it working yet. You can also program your aura specifically to protect you from these attacks. Your Guardian Demon will also protect you from anything too serious, until you are advanced enough to protect yourself.
I think your worrying about too much stuff right now. They can do this but why would they. Ask yourself that and relax. The enemy may not have all the abilities to make sense of these things anyways even if they can read them as they are a hive mind they don't think or react quickly or have their own thoughts. It's kind of like the hive has to decide to do something to you or something like that not sure I understand all of it. Dont give them too much attention.
By sensing their energy and/or looking at their soul. Often looking a person in the eyes is enough to form a weak connection to them and sense their energy.
Those who are with the enemy will have a soul loaded with disgusting energy, and it's actually pretty obvious when you get experienced at feeling energy. This is a much more basic skill than seeing energy. You can do this even if your astral vision is still closed. All you need a quiet mind and a basic ability to feel energy, which you can improve with the Circulating Energy meditation.
When I was a child, in every school class there were always one or two kids who I inexplicably believed were "enemies". I spent a lot of time thinking about what's different about them and why it feels so rotten interacting with them. Now I just look back at their pictures, and say "Oh, they're jews, of course." It turns out that I was always able to feel energy as a child; I just never knew what it was!
Satanists and those who are genuinely seeking truth will feel "clean", so to speak, because their energy's vibration is similar to yours.