Learn Dutch: Niemand weet wie de dader helpt. - No one knows who is helping the perpetrator.

The phrase wie de dader helpt is an indirect question. In Dutch, indirect questions follow the exact same word order rules as subclauses, which means the conjugated verb gets pushed to the very end.

Could wie de dader helpt also mean "who the perpetrator is helping"?

Yes, it technically could! Because Dutch doesn't change the spelling of the noun de dader or the question word wie to show who is the subject and who is the object, it can be slightly ambiguous. However, Dutch usually puts the subject first, so listeners will naturally assume wie is the one doing the helping unless context strongly suggests otherwise.

Why do we use weet and not weten for Niemand?

Just like the English words "no one" or "nobody", the Dutch pronoun niemand is grammatically singular. That is why it takes the singular verb weet rather than the plural weten.

Does the word dader come from another Dutch word?

Yes, it is built from the noun de daad (the deed or action) and the suffix -er (a person who does something). A dader is literally a "doer" of a deed, though in modern Dutch it is almost exclusively used to mean a perpetrator or culprit.