Here ons means us.
Afrikaans uses ons for both we and us, so you work it out from the sentence structure. In Die boek gee ons kennis, ons comes after the verb and receives the action, so it means us.
Because Afrikaans often uses the pattern gee iemand iets, which means give someone something.
So:
The recipient can come directly after the verb without aan. You can use aan in some other sentence patterns, but in this normal structure it is not needed.
Here kennis means knowledge in a general, uncountable sense. Uncountable nouns often appear without an article, just as in English.
A useful contrast is:
So in this sentence, no article is used because kennis is not a countable item.
The structure is:
So the pattern is:
subject + verb + recipient + thing given
This is a very common pattern with gee in Afrikaans.
A simple way to check is to ask two questions:
The thing being given is the direct object, and the recipient is the indirect object. So:
A natural past-tense version is:
Die boek het ons kennis gegee.
Afrikaans usually forms the past tense with het + past participle.
Here:
Notice that gegee moves to the end of the clause.