Breakdown of Chcę poznać twojego brata.
chcieć
to want
brat
brother
twój
your
poznać
to meet, to get to know (perfective)
Questions & Answers about Chcę poznać twojego brata.
Why is poznać used here instead of znać?
Znać means to know someone, which describes an ongoing state. Poznać means to get to know or to meet someone for the first time. Because you are talking about the action of meeting him, you use the perfective verb poznać.
Why does the sentence use twojego brata instead of twój brat?
Twój brat is the subject form (nominative). Here, the brother is the direct object of the verb poznać, which requires the accusative case. For masculine living things like people and animals, the accusative case looks exactly like the genitive case, so twój brat changes to twojego brata.
Why does the word twój change all the way to twojego?
Twój (your) is a pronoun, and it must match the noun it describes. Just like brat takes the -a ending to become brata, the pronoun must also change to its matching accusative/genitive form, which is twojego.
Can poznać mean anything else besides getting to know someone?
Yes. Depending on the context, poznać can also mean to recognize someone or something. For example, if you were looking at a blurry photo, this same verb could be used to say you want to recognize him, though to meet or to get to know is the most natural meaning for this specific sentence.