I am not sure I understand the question. "Lightning" has two syllables-- light, and ning. Nothing else was added to it. The word is a noun, referring to flashes of electricity in the sky during a storm, often accompanied by the loud sound of thunder.
Lightning is stressed on the first syllable.
Lightning is a two syllable word spoken as light-ning.
The first syllable
Yes, lightning is two syllabels: light-ning.
Neither it is an added syllable
A prefix is a syllable that is added to the beginning of a word to change its meaning or create a new word.
prefix
prefix
prefix
The syllable added to the end of a word is called a suffix. It can modify the meaning or change the grammatical function of the word.
Disastrous has three syllables but, yes, an extra syllable is often added in speech due to the relationship between this word and the word disaster.
A "prefix". However, note that some prefixes, such as "ante" and "anti", have more than one syllable.