* τι (ti): This is the most common translation and is used for the interrogative pronoun "what" meaning "what thing?" or "what matter?". It's used for direct questions about things or matters. For example, "Τι είναι αυτό;" (Ti ine aftó?) means "What is this?".
* ποιο (poio), ποια (poia), ποια (poia): These are used when asking "which" or "what kind of". They are declined according to gender and number (poio is masculine singular, poia is feminine singular and neuter plural, poia is feminine plural). For example, "Ποιο βιβλίο διάβασες;" (Poio vivlio diabases?) means "Which book did you read?".
* πως (pos): This translates to "how" or "in what way," but can also be used when asking about something's state or condition. For example, "Πως είσαι;" (Pos eisai?) means "How are you?". While not directly "what", it's a contextual equivalent depending on the question.
To give you the best Greek translation, please provide the full English sentence containing "what."