I would like to know some word choices (can be a noun, adjective,...) for not knowing about something,
For example, I guess ignorant/ignorance is a negative word, is it? Can I use it to describe myself before asking others (especially experts) a question, to show that I am humble?
You are right that ignorant/ignorance often carries a negative sense ("He's so ignorant!"), but it can also be used neutrally ("Ignorant of what had happened in my absence, I continued as before"). It can certainly be used to express humility ("Forgive my ignorance, but who is the current president of South Korea?").
For the neutral sense there is also unaware (and unawareness).
There are not many emphatically positive expressions for lack of knowledge, since this is usually considered a negative (though you might argue innocent has this sense; also ignorant and unaware are often combined with blissfully, after the proverb Ignorance is bliss). But there are expressions for situations where lack of knowledge is expected, and therefore perhaps less negative — for instance, novice, apprentice, learner, beginner, and if your aim is to express humility then any of these would be appropriate.
negative
neutral.
positive.
The first thing that comes to my mind is Emotional Intelligence.
Uninformed is fairly neutral, as is unenlightened. Words like novice or freshman describe someone new to some role, and, by implication, not yet highly knowledgeable. I would say those are a bit more positive. No apology is needed for someone who is trying to learn. You can't know something before you know it, and asking questions is one way to gain knowledge and learn. Anyone who is expert in a subject had to first learn it and had to have started from a state of being less knowledgeable.
What about naïve?
Lacking worldly experience, wisdom, or judgment; unsophisticated.
Very absent-minded, not knowing what your surroundings are, other focuses, not concentrated.
