Learn Romanian: Eu îl cunosc pe șeful tău.

This is a special Romanian rule for direct objects. When the object of your sentence is a specific person (like șeful tău - your boss), Romanian does two things: it puts the word pe right before the person, and it adds an extra short pronoun before the verb. Literally, the structure looks like "I him know on the boss your."

Why use "îl" specifically? Could I leave it out?

You cannot leave it out when using pe for a specific person. îl is the masculine singular short pronoun for "him". We use it because șeful (the boss) is masculine and singular. If you knew a female boss (șefa), you would use the feminine pronoun o: Eu o cunosc pe șefa ta.

Why use "cunosc" for "I know" here? Can I use "știu"?

No, you must use cunosc here. Romanian has two verbs for "to know". A ști is for knowing facts, skills, or information (like "I know the answer"). A cunoaște (which becomes cunosc for "I") is used for knowing people, being acquainted with a place, or recognizing something. Since you know a person here, you have to use cunosc.

Why is it "șeful tău" and not just "șef tău"?

In Romanian, when you use a possessive word like tău (your), the noun before it must usually have the definite article attached to the end of it. Șef means "boss", and adding -ul makes it șeful (the boss). So, Romanian literally phrases it as "the boss your".