Learn Polish: Znam twojego ojca. - I know your father.

In Polish, the direct object of a sentence takes the accusative case. For masculine nouns that are alive (like a person or an animal), we add an -a to the noun and change the describing word like twój to end in -ego. This is why the basic form twój ojciec becomes twojego ojca here.

Why does ojciec become ojca? Where did the e go?

The word ojciec has a disappearing e. When we add an ending to it (like the -a for the accusative case), that last e drops out to make the word easier to say. So, instead of saying ojcieca, it simply becomes ojca.

Could I use wiem instead of znam to say I know?

No, because Polish has two different verbs for knowing. You use znać (which gives us znam) when you know a person, a place, or a thing. You use wiedzieć (which gives us wiem) when you know a fact or a piece of information. Since you know a person here, you must use znam.

Why isn't there a Polish word for I at the beginning of the sentence?