Learn Dutch: Hebben jullie vaak zulke overstromingen meegemaakt?

We use zulke because overstromingen (floods) is plural. The word zo'n translates to "such a", so it is only used with singular countable nouns (like zo'n overstroming). For plural nouns or uncountable nouns, you must use zulke (such).

What is the dictionary form of meegemaakt, and why is it at the very end of the sentence?

The infinitive is meemaken (to experience or live through). This sentence uses the present perfect tense. In Dutch yes/no questions, the helping verb (hebben) comes first, and the past participle (meegemaakt) is pushed to the very end of the sentence.

Is meemaken a separable verb?

Yes! It consists of the prefix mee and the verb maken. When forming the past participle, the ge- is placed between the two parts, which is why it becomes mee-ge-maakt.

Why does vaak (often) come before the direct object zulke overstromingen?

In Dutch, adverbs of time and frequency (like vaak) generally come right after the conjugated verb and subject. They almost always appear before a direct object, unlike in English where "often" can sometimes float to different parts of the sentence.