Learn French: Tu pourras voir le documentaire dont nous avons besoin. - You will be able to see the documentary that we need.

In English, we say "the documentary that we need", so it's very tempting to use que. However, in French, the expression for "to need" is avoir besoin de. Because this expression requires the preposition de, you must use the relative pronoun dont to link it back to le documentaire.

Where did the de from avoir besoin de go?

It was absorbed by dont! The word dont essentially means de plus the thing you are referring to. Adding de at the end of the sentence (dont nous avons besoin de) is a common mistake for English speakers, but it is redundant. It would be like saying "the documentary of which we have need of".

What tense is pourras?

Pourras is the future tense (futur simple) of the irregular verb pouvoir (to be able to, can). It translates to "will be able to". Notice that it is followed directly by the infinitive voir (to see) without any extra prepositions in between, just like it is in the present tense.

Could I say dont on a besoin instead of dont nous avons besoin?