Differently from Italian and many other Romance languages, the venetan apostrophe performs two functions at the same time:
1. it indicates that a vowel or
a consonant has been dropped in a word and
2. it tells the correct pronunciation of the shortened word
The only rule is that «the apostrophe indicates the direction towards which the shortened word must be attached» when pronouncing it.
So, if the apostrophe is at the left side of a consonant this must be pronounced as FINAL consonant of the word at its left side (automatically, when an apostrophe is at the right side, the consonant is pronounced as INITIAL consonant of the word at its right side).
In Venetan, for example, the letter -n has two pronounciations because it is velar (like English -ng) when it is at the end of a word, whereas it is dental in the other instances.
For example the article "UN" can be apostrophized in two ways («'n / n'») according to the pronounciation:
In the first case the -n is
pronounced as final consonant of the previous word,
i.e. it is a "velar N"
In the second case the -n is pronounced as initial consonant of the following word, i.e. it is a "dental N"
The same pattern is followed by the article "EL", apostrophized as « 'l / l'» according to the pronounciation:
Even the obligatory subject pronoun "EL" follows this rule when a negation "NO" is involved; let's see an example with the verb xe/č is (in the long and the short forms):
Generally, when you apostrophize an article/pronoun you «write the apostrophe at the right side when the following consonant begins with a vowel» (it'll be automatically placed at the left side if the other cases).
The "apostrophe rule" also works with dropped consonants, as for example:
The apostrophe is at the left side and the apostrophized word 'ito said joins the verb "ň" I have at its left side.
However, in some Venetan variants, you need not apostrophize the words so you just skip this rule.