Questions & Answers about Что вы ему купили?
Why does this sentence use ему instead of его?
ему is the Dative case of он (he). In Russian, the person receiving an action or having something done for them takes the Dative case. Since you are buying something for him, you use ему rather than the Accusative его.
Can I change the word order and say "Что вы купили ему?"
Yes, absolutely! Russian word order is very flexible. Putting the pronoun ему before the verb купили is just a very common and natural way to speak, but putting it at the end is also perfectly correct.
Why does the verb купили end in -ли?
This is the past tense. In Russian, past tense verbs change to match the gender and number of the subject. Since the subject here is вы (you, formal or plural), the verb takes the plural past tense ending -ли.
As a quick reminder, why is Что pronounced with an "sh" sound?
It is a historical exception you just have to memorize! Even though it starts with the letter Ч (which normally makes a "ch" sound), the word Что (what) is always pronounced "shto".