Learn Dutch: Ik ken de slager die dit vlees verkoopt. - I know the butcher who sells this meat.

In Dutch, we use die to say 'who' or 'that' when referring back to a de-word or a plural word. Since slager (butcher) is a de-word (de slager), we use die to connect the sentences.

Why is the verb verkoopt at the very end of the sentence?

The part of the sentence starting with die gives extra information about the butcher. This is called a relative clause. In Dutch, relative clauses always push the working verb (verkoopt) to the very end of that clause.

Could I say Ik weet de slager instead of Ik ken de slager?

No, you must use kennen here. In Dutch, kennen is used for being familiar with people, places, or things. The other verb for 'to know', weten, is only used for knowing facts or information (like knowing what time the shop opens).

Why is it dit vlees and not deze vlees?

Vlees (meat) is a het-word (het vlees). When you want to say 'this' with a singular het-word, you always use dit. If it were a de-word or a plural word, you would use deze.