General "what":
* क्या (kyā): This is the most common and versatile way to say "what." It can be used in questions, exclamations, and even as a filler word.
* कौन (kaun): This is used when asking about a person or thing. For example, "Who is that?" would be "वह कौन है?" (vah kaun hai?).
For specific situations:
* क्या (kyā): This is used for questions about an object or situation. For example, "What is that?" would be "वह क्या है?" (vah kyā hai?).
* कैसे (kaise): This is used for questions about how something is done. For example, "What is this?" would be "यह कैसे है?" (yah kaise hai?).
* क्यों (kyon): This is used for questions about why something happened. For example, "What happened?" would be "क्या हुआ?" (kyā huā?) or "क्यों हुआ?" (kyon huā?).
Examples:
* क्या तुम समझते हो? (kyā tum samajhte ho?) - Do you understand?
* कौन आया है? (kaun āyā hai?) - Who has come?
* यह क्या है? (yah kyā hai?) - What is this?
* तुम क्या कर रहे हो? (tum kyā kar rahe ho?) - What are you doing?
* कैसे हुआ? (kaise huā?) - How did it happen?
* क्यों रो रहे हो? (kyon ro rahe ho?) - Why are you crying?
It's important to note that the specific word you use will depend on the context of the sentence.