Not only is this word not in the dictionary, there is not a single instance of it on all the millions of websites searched by Google. '-ness' is often added to adjectives to form nouns meaning a state or a quality, for example politeness – the quality of being polite; happiness – the state of being happy. However, initiative is a noun, not an adjective, so in this case the suffix is redundant: initiative already means "the quality of being able to decide independently what to do and when to do it".

If you wanted to make the sentence even more explicit than it already is, you could say "… your use of initiative/your ability to use your initiative in …".

Why can one say I heard about that but not I listened about that?

Like many frequent words, both listen and hear have more than one meaning. While their 'core' meanings relating to perceiving with your ears are similar and often confuse learners, I don't think those are the meanings being used here. Hear has several different meanings and the one that is being used when we say "I heard about that" is the one that means something like learn. The Macmillan English Dictionary defines it as "to receive information about something". When you use this meaning of hear you are not necessarily referring to the use of your ears at all – you could hear about something via email or in a letter or by reading a newspaper. Listen, on the other hand, means "to pay attention to a sound or to try to hear a sound" – it refers to a physical sensory act rather than to receiving information.

Hear plus about is a very significant combination; you could almost treat it as a single unit of meaning. I was going to say that listen about does not occur as a unit, but in fact it does, although it is not that frequent and I was not familiar with it. It seems to mean that someone pays attention to someone or something (or often that they don't), or sometimes just the same as listen to. I found these examples using Google:

They are not even prepared to listen about other religions.
He mostly seems to want to sing about heroin and gangstas, and I don't really want to listen about heroin and gangstas.
You could watch and listen about hockey until your brain overloads.

I read a lot of books about pronouncing fractions. They are very different. Can you tell me the clear way to pronounce them?

The reason you are finding different ways of pronouncing fractions is because there are different ways of pronouncing them, which are equally correct. The basic rule is that you use the ordinal form of the number (the one that usually ends in 'th', like fifth and ninth) for the bottom number and the cardinal form (for example three or four) for the top, and you pluralise the ordinal number:

When the top number is 1 you can use a or one:

When the bottom number is 2, you use half (not second):

When the bottom number is 4, you can use either fourth or quarter. Fourth tends to be more common in American English and quarter in British English, but both are used in both: