"Why don't you drink anything?"
Translation:Warum trinkst du nichts?
As quis_lib_duo said, wieso, weshalb, warum are synonyms. And I guess, every German who saw sesame street in his infancy still remembers the lines of the intro, encouraging children to be curious and to ask: Wieso, weshalb, warum - wer nicht fragt, bleibt dumm!
As to the variants of who/whom: They depend on the four grammatical cases. Wikipedia has a good explanation of those. The correlating questions to the examples on Wikipedia would be:
Der Seemann steht da - Wer steht da?
Der Name des Seemannes ist Otto - Wessen Name ist Otto?
Ich gab dem Seemann ein Geschenk - Wem gabst du ein Geschenk?
Ich sah den Seemann - Wen sahst du?
Well, I can try another approach.
In this exercise, "not...anything" had to be translated.
"Not anything" or "nothing" both translate to "nichts" in German.
Effectively, of course, the outcome will be the same whether someone does not drink at all or whether someone does not drink anything. No beverage will be swallowed.
But semantically, it is not the same. One could further specify the negation:
I don't drink anything from a given choice: "Ich trinke nichts davon."
I don't drink when I'm alone: "Ich trinke nicht allein."
Because this order would not fit.
"Etwas" modifies following nouns, adjectives or adverbs. In your sentence, "etwas" would modify "nicht" which does not make much sense.
For instance, one could say "Du trinkst etwas zu schnell" (You're drinking a bit too fast")
Thus, the correct order would be "Warum trinkst du nicht etwas?" which is further shortened to "Warum trinkst du nicht(s)?"
I'm sorry for probably having mislead you by not expressing my thoughts well enough.
The phrase you chose would sound rather strange in German, it would be kind of a too literal translation.
In this case, when somebody asks why another person doesn't drink anything at all, the correct question can be "Warum trinken Sie nichts" or "Warum trinkst du nichts".
In German, there's a hard “(conjugated) verb second) rule” in main clauses (the only exception being yes/no question, where the verb is in first position). In questions, the interrogative (adjective/pronoun/adverb/phrase) generally has to come first, so the verb must follow immediately (to follow the above rule), so “warum trinkst” must be the first two words. After that, the subject would take the first available position.
In declarative sentences, the unmarked version would put subject first (“du trinkst Bier”), but emphasised elements can take the first place, necessarily displacing the subject, yielding sentences like “heute trinkst du Bier” (emphasis on today).