Was? Was?
Same word, two cases.
Wer? and Wen? are two different words for two different cases. Was? is not. For things and ideas, the very same word covers both the Nominativ and the Akkusativ. The word never changes. Only the box around it does, yellow or green, depending on what was is doing in the sentence.
Related: Ask Wer? Find the subject. (Nominativ) and Ask Wen? Find the object. (Akkusativ).
Was? for things, the Akkusativ job
The job you'll meet first → Was? asks for the direct object when the object is a thing rather than a person. Someone is already doing something, the action lands on a thing, and that thing is Akkusativ. In edupango, that's green.
- Er liestdasBuch. Was liest er? → dasBuch.
- Sie trinkteinenKaffee. Was trinkt sie? → einenKaffee.
Notice the shape → subject + verb + thing. Was? points at the thing, and the thing is green. This is exactly the same job Wen? does for people.
Was? for things, the Nominativ job
Here's the part that trips learners up → Was? can also ask for the subject itself, when the subject is a thing. There is no separate person doing something to it, the thing itself is the one doing or being something. That makes it Nominativ, which edupango marks in yellow.
- Was ist das? → Das isteinComputer. (What is that? That is a computer.)
- Was passiert hier? → EinUnfall passiert hier. (What's happening here? An accident is happening here.)
Notice the shape this time: there's no other actor in the sentence. Was? itself is the one doing or being something, so it stays yellow, just like Wer? does for people.
The test: is was doing it, or having it done to it?
One quick question settles the color every time. Look at the sentence and ask: is there already a subject acting, with was just sitting there receiving the action? Then was is the object, Akkusativ, green. Or is was itself the one doing or being something, with no other subject in sight? Then was is the subject, Nominativ and yellow.
- Was ist das? → Nominativ. Nothing else is acting, was is the thing itself.
- Was siehst du? → Akkusativ. du is already the subject, was is what you see.
The takeaway → Was? and Was? are the same word, never two forms to learn. Check the sentence for an existing subject. If one is already there, acting on the thing, was is green. If the thing itself is the subject, was is yellow.