Learn Dutch: Wat voor dieren zijn meestal tam? - What kind of animals are usually tame?

Welke means "which" and is used when you are asking about specific choices from a known group (e.g., "Which animals at this zoo are tame?"). Wat voor means "what kind of" or "what sort of", asking for a general category. Here, you want to know the category of animals that are usually tame, so wat voor is the correct choice.

I learned this phrase as wat voor een. Why is een missing here?

You use wat voor een with singular nouns (like wat voor een dier - "what kind of animal"). Because dieren (animals) is plural in this sentence, we drop the een (a/an). Just like in English, you wouldn't say "what kind of an animals".

Why does the verb zijn come after the whole phrase Wat voor dieren?

In Dutch questions, the verb must immediately follow the question word or phrase. Here, Wat voor dieren acts as one inseparable block of information. The verb zijn takes the second position in the sentence right after that block.

Why doesn't the adjective tam get an -e added to the end?

Adjectives usually only get an -e ending when they come directly before a noun (for example, tamme dieren). Because tam is separated from the noun and comes after a verb like zijn (to be), it stays in its basic, uninflected form.