Learn Swedish: Vad händer nu? - What is happening now?

Swedish doesn't have a continuous tense (like "is happening"). The simple present tense händer translates to both "happens" and "is happening". You should never use är (is) right before another verb to say what is currently going on!

I often hear native speakers drop the "d" in vad. Is that normal?

Yes! In spoken Swedish, the d in vad is almost always silent, so it sounds exactly like "va". You will generally only hear the d in very formal or careful speech.

What is the infinitive (dictionary form) of händer?

The infinitive is att hända (to happen). To form the present tense of verbs in this group, you drop the final -a and add -er, which gives us händer.

Since this is a question, shouldn't the verb come first?

In yes/no questions, the verb does come first. But in this type of question, the question word vad (what) acts as the subject. Swedish puts the verb in the second position, so händer comes right after the subject, just like in English!