"Tu" can be added for emphasis, which changes the meaning a bit. Something like:

• Vedi tu il pescatore? = Are you the one that sees the fisherman?

I sense that what you need to know from this question and from your posting "Do you work as an engineer" is that the indefinite article is not used when saying what someone's job is.

To say what someone's job is you leave out the article: è medico ( he is a doctor) OR you can use the verb fare with the definite article: faccio l'ingegnere (I'm an engineer)

Beyond that, it's probably best to pick up a grammar book and check out when to use or not to use the articles, however, some general points might help:

1) Definite articles are used more in Italian than in English. 2) Italian sentences do not usually start with a noun without an article. 3) You need to use article with parts of the body and with time, unlike English 4) Indefinite articles are not used when saying what someone's job is. 5) Indefinite articles are not used with the numbers "cento" and "mille"

Hope this helps!

It could be the plural form of you but that would be vedete. Vedono is they see.

• (tu) vedi il pescatore? = Do you see the fisherman? (singular, informal)
• lei vedi il pescatore? (wrong conjugation)
• (lei) vede il pescatore? = Does she see the fisherman?
• (Lei) vede il pescatore? = Do you see the fisherman? (singular, formal, only with capital case Lei)

Word order is very important in Italian, it's usually Subject-Verb-Object, even in questions:

• il pescatore vede? = does the fisherman see?
• il pescatore vedi? = do the fisherman see? (with wrong conjugation)
• (tu) vedi il pescatore? = do you see the fisherman?

Seeing and watching are not synonymous.