The Russian word for ‘what’ is что. Although it is written with the letter ч, the nominative/accusative form of the word is most commonly pronounced [што]; in the other cases we do pronounce ч as ч. It occurs in all six cases:

Notice that the only difference between the prepositional and instrumental forms is the двоеточие “double dots” over the prepositional form.¹ Remember that the Russians usually do not usually write the double dots, so context will have to tell you how to pronounce those forms. Some sample sentences:

Somewhere in school every American is taught the rule “never end a sentence with a preposition.” For English it's an assinine rule that has no reasonable justification in the living language.² However, for Russian the rule is real and alive. It's not an artificial rule, as in English, but rather a subconscious part of the living language: no Russian will ever end a sentence with a preposition, not even accidentally. So whenever you are translating a question from English to Russian, and the question ends with a preposition, you need to move that preposition to before its object and then translate. Thus:

Other examples:

Notice in the last example we can leave the preposition out of the response in English, but in Russian you must retain the preposition to justify the case of памятник.

¹ The double dots symbol is often called a diaeresis or an umlaut. The former is theoretically used to indicate that a vowel is pronounced as a complete vowel (not a diphthong) when preceded by another vowel with which it might blend. The latter is theoretically used to indicate that vowel is fronted. Since neither of those instances prevails in the е/ё distinction, “double dots” is a sensible name for the symbol.

² Of course, one can't mention this rule of English without mentioning Winston Churchill's famous definition: “A preposition is a word you can't end a sentence with.” I actually doubt that Churchill said it, but it's too fun not to mention.