I suffix comes at the end of the word to change its meaning such as -ity, -ness, -ment. An abstract noun is something you can't see, hear, touch, feel, or smell. It is not concrete. So, in order to add to each of these, you must add a suffix at the end of the word to make it abstract. For example, if given the noun fellow, you can add the suffix -ship to form 'fellowship', which is now an abstract noun. Look at suffixes -ship, -less, and -ness to help you.
For the second part, you need to use a word that replaces the underlined words that has a prefix (like re-, extra-, in-) or a suffix.